Learn Hardcore Polish: Wieczorem lubię spacerować po parku z psem. - In the evening I like to stroll in the park with the dog.

Lubię means I like.
- The ending -ę tells you the subject is ja (I).
So Ja lubię spacerować… would be correct, but sounds a bit heavy or emphatic in normal conversation.
The most natural version is simply: Lubię spacerować po parku z psem.

Use ja only for emphasis, e.g.:

Ja lubię spacerować po parku, ale on woli siedzieć w domu.
I like walking in the park, but he prefers staying at home.

Why is it lubię spacerować and not something like lubię spaceruję?

After the verb lubić (to like), Polish uses the infinitive of the second verb:

lubię spacerować = I like to walk / walking
lubię czytać = I like to read / reading
lubię gotować = I like to cook / cooking

You do not conjugate the second verb here.
So lubię spaceruję is ungrammatical. It must be:

lubię + [infinitive] → lubię spacerować

What is the difference between lubię and kocham?

Both can translate as like/love, but they’re used differently:

lubić = to like (general preference, enjoyment)
- Lubię spacerować po parku. – I like walking in the park.
- Lubię kawę. – I like coffee.
kochać = to love (strong emotional attachment, mostly people, sometimes things)
- Kocham mojego psa. – I love my dog.
- Kocham cię. – I love you.

In this sentence you’re talking about an activity you enjoy, so lubię spacerować is the natural choice, not kocham spacerować (which would sound exaggerated or a bit odd).

Why is it wieczorem and not w wieczór?

Polish often uses a bare noun in the instrumental case to say “in the [part of the day]”:

rano / rankiem – in the morning
po południu – in the afternoon
wieczorem – in the evening
nocą – at night

Wieczorem is the instrumental singular of wieczór (evening), and in this time expression you don’t add a preposition like w.

So:

Wieczorem lubię spacerować… = In the evening I like to walk…
W wieczór is not used in this meaning.

What’s the difference between wieczorem and wieczorami?

Both refer to evenings, but there is a nuance:

wieczorem – in the evening (can be one specific evening or a general habit)
wieczorami – in the evenings, on evenings in general, more clearly habitual

Examples:

Wieczorem lubię spacerować po parku.
I like walking in the park in the evening. (could be understood as a general habit)
Wieczorami lubię spacerować po parku.
I like walking in the park in the evenings. (more strongly habitual, “evenings in general”)

Both are correct here; wieczorami just emphasizes the routine a bit more.

Why is it po parku and not po park or w parku?

There are two separate issues:

Case after preposition “po”
The preposition po usually takes the locative case:
- po parku (locative of park)
- po ulicy (along the street)
- po domu (around the house)
So po park is wrong; you must say po parku.
Meaning: “po” vs “w”
- spacerować po parku – to walk around/through the park, moving about inside it
- spacerować w parku – to walk in the park (also correct, but slightly less focused on moving around the area)

In practice, spacerować po parku is a very natural, common collocation for walking around the park.

Why is it parku and not park?

Parku is the locative singular form of park.

The preposition po in this sense (moving around an area) requires the locative case:

po parku – in/around the park
po mieście – around the city
po lesie – in/around the forest

So the pattern is:

Nominative: park
Locative: w parku, po parku

That’s why you see parku here.

Why is it z psem and not z psa or z piesem?

After z in the sense of with (someone), Polish uses the instrumental case.

Pies (dog) declines like this (singular):

Nominative: pies – a dog
Accusative: psa – I see a dog (widzę psa)
Instrumental: psem – with a dog (z psem)

So:

z psem – with a dog (correct: instrumental)
z psa – wrong here; psa is accusative
z piesem – incorrect form; the proper instrumental is psem

What case is used in wieczorem, po parku, and z psem, and why?

Each form uses a different case with its own function:

wieczorem – instrumental (singular)
Used as a time expression: “in the evening”.
po parku – locative (singular)
Required by the preposition po when it means “around/through” a place.
z psem – instrumental (singular)
Required by z when it means “with (someone/something)” as a companion.

So the structure is:

[Instrumental of time]
- lubię
  - [infinitive]
    - po
      - [locative]
        z
        [instrumental]

Can I change the word order? For example: Lubię wieczorem spacerować po parku z psem?

Yes. Polish word order is flexible, and your example is natural.

Some common variants (all correct, slightly different emphasis):

Wieczorem lubię spacerować po parku z psem.
Neutral: emphasis a bit on when (in the evening).
Lubię wieczorem spacerować po parku z psem.
Neutral: starts with what you like.
Lubię spacerować wieczorem po parku z psem.
Emphasis that the walking (not some other activity) happens in the evening.

All of these are fine in everyday Polish. The main rules are:

lubię must agree with the subject
spacerować must stay in the infinitive
po must go with parku
z must go with psem

What is the aspect of spacerować, and why isn’t it pospacerować?

Spacerować is imperfective (ongoing, repeated, habitual).
Pospacerować is perfective (a completed act of walking for some time).

With lubić, you normally use the imperfective infinitive because you are talking about a general habit or liking, not one finished event:

Lubię spacerować po parku. – I like walking in the park (in general).
Chcę pospacerować po parku. – I want to have a walk in the park (one completed walk).

So here spacerować is the appropriate choice.

How would I say the same sentence in the past or future?

You only need to change lubię and keep spacerować in the infinitive:

Present:
Wieczorem lubię spacerować po parku z psem.
In the evening I like to walk in the park with my dog.
Past (masculine speaker):
Wieczorem lubiłem spacerować po parku z psem.
Past (feminine speaker):
Wieczorem lubiłam spacerować po parku z psem.
Future (using future of lubić):
Wieczorem będę lubił spacerować po parku z psem. (male)
Wieczorem będę lubiła spacerować po parku z psem. (female)

In practice, for preferences people more often talk in the present, but these forms are grammatically correct.

How would I put park and dog in the plural, keeping the same structure?

You keep the same prepositions and cases, but use plural forms:

po parkach – around parks (locative plural of park)
z psami – with dogs (instrumental plural of pies)

Example:

Wieczorem lubię spacerować po parkach z psami.
In the evenings I like walking around parks with dogs.

Usually you’d say something more natural like:

Wieczorem lubię spacerować po parku z moimi psami.
…in the park with my dogs.

How should I pronounce wieczorem lubię spacerować po parku z psem? Any tricky sounds?

Main points:

wie in wieczorem – like vye.
cz – one sound, like ch in chocolate, but harder: wie-czo-rem.
lubię – lu-by-ę:
- ó sounds like English oo in boot.
- Final -ę is often pronounced very softly in speech, almost like -e.
spacerować – spa-ce-ro-vać:
- c = ts (like cats).
- Final -ć is soft, somewhat like t but palatalized.
z psem – pronounced almost like one unit: zp-sem, with ps cluster as in psychology.

Syllable breakdown: wie-czo-rem lu-bię spa-ce-ro-wać po par-ku z psem.

Is there another common way to say “I like to walk in the park in the evening with my dog”?

Yes, a few natural alternatives:

Wieczorem lubię chodzić na spacer z psem do parku.
Literally: In the evening I like to go for a walk with my dog to the park.
Wieczorem lubię chodzić z psem po parku.
In the evening I like walking around the park with my dog.
Lubię wieczorne spacery z psem po parku.
I like evening walks with my dog in the park.

Your original sentence is already perfectly natural; these just show other common patterns.