Po spacerze daję psu mały smakołyk, kiedy spokojnie czeka przy drzwiach.

Because po in the sense of after requires the locative case in Polish.

• spacer = walk
• po spacerze = after the walk / after a walk

So the noun changes form:

• nominative: spacer
• locative: spacerze

This is a very common pattern:

• po obiedzie = after lunch
• po pracy = after work
• po filmie = after the film

Daję is the 1st person singular present tense of the imperfective verb dawać = to give.

It is used here because the sentence describes a habit, routine, or repeated action:

• Po spacerze daję psu mały smakołyk = After the walk, I give the dog a small treat.

If you said dam, that would be the future of the perfective verb dać:

• Dam psu smakołyk = I will give the dog a treat.

So:

• daję = I give / I am giving / I usually give
• dam = I will give

Because the dog is the recipient of the treat, so Polish uses the dative case.

• basic form: pies = dog
• dative form: psu = to the dog

In this sentence:

• daję psu smakołyk = I give the dog a treat

This is very typical with verbs like dawać:

• daję dziecku książkę = I give the child a book
• pokazuję koledze zdjęcie = I show my friend a photo

A useful pattern is:

ktoś daje komuś coś
someone gives someone something

So:

• komu? → psu
• co? → mały smakołyk

Because mały smakołyk is the direct object of the verb daję, and with this kind of noun it looks the same as the nominative.

• smakołyk = treat, delicacy
• mały smakołyk = a small treat

Here it is in the accusative case, because it is the thing being given:

• daję co? → mały smakołyk

For this masculine inanimate noun, the accusative singular is the same as the nominative singular:

• nominative: mały smakołyk
• accusative: mały smakołyk

So nothing changes in form, even though the grammatical case has changed.

Polish does not have articles like English the and a/an.

So:

• pies can mean dog, a dog, or the dog
• smakołyk can mean a treat or the treat

The exact meaning depends on context.

In this sentence:

• psu is naturally understood as the dog / my dog from context
• mały smakołyk is understood as a small treat

Polish usually does not need an article system because case endings and context do a lot of that work.

The subject is understood, not stated explicitly. In context, he = the dog.

So:

• kiedy spokojnie czeka przy drzwiach = when he waits calmly by the door

Polish often omits subject pronouns when the meaning is clear from context.

Here:

• daję already tells you I
• czeka means he/she/it waits
• from the sentence, it is clear that the dog is the one waiting

So a more literal English version would be:

• After the walk, I give the dog a small treat when he waits calmly by the door.

Because spokojnie is an adverb, while spokojny is an adjective.

Here we are describing how the dog waits:

• czeka jak? = waits how?
• spokojnie = calmly

Compare:

• spokojny pies = a calm dog
  
  • adjective describing the noun pies
• pies czeka spokojnie = the dog waits calmly
  
  • adverb describing the verb czeka

So spokojnie is correct because it modifies the action, not the dog directly.

Because przy means by / near / next to, and it requires the locative case.

• drzwi = door / doors
• przy drzwiach = by the door

A few examples:

• przy stole = by the table
• przy oknie = by the window
• przy ścianie = by the wall

So the structure is:

• przy + locative

That is why you get drzwiach, not drzwi.

Because drzwi is one of those Polish nouns that is plural in form, even when it refers to a single door.

This is called a plural-only noun.

So:

• basic form: drzwi
• locative after przy: drzwiach

Other common plural-only nouns include:

• nożyczki = scissors
• spodnie = trousers
• okulary = glasses

So even if English uses singular door, Polish uses the noun drzwi, which behaves grammatically like a plural noun.

It can suggest either, depending on context, but in this sentence it most naturally has a habitual sense: when / whenever.

Because the main verb is daję, which suggests a repeated routine, the whole sentence sounds like:

• After a walk, I give the dog a small treat when(ever) he waits calmly by the door.

So kiedy here is not just a one-time event marker. It fits a repeated situation.

If you wanted to make the habitual meaning even clearer, context would usually do that, but the sentence already strongly suggests it.

Yes, the word order is natural, and yes, it could be changed.

Current version:

• Po spacerze daję psu mały smakołyk, kiedy spokojnie czeka przy drzwiach.

This is clear and idiomatic.

But Polish word order is more flexible than English because case endings show grammatical roles. For example, you could also say:

• Po spacerze daję mały smakołyk psu, kiedy spokojnie czeka przy drzwiach.
• Psu daję mały smakołyk po spacerze, kiedy spokojnie czeka przy drzwiach.

These alternatives may shift emphasis slightly:

• psu earlier = stronger focus on the dog
• mały smakołyk earlier = stronger focus on the treat

Still, the original sentence sounds very normal.

Not with exactly the same meaning.

• po spacerze = after the walk / after going for a walk
• po wyjściu = after leaving / after going out
• po chodzeniu = after walking, but this sounds less natural in this context

Spacer specifically means a walk as an outing, often leisurely or routine, which fits perfectly here.

So if you mean a normal dog walk, po spacerze is the best and most natural choice.

Czeka comes from czekać, which is an imperfective verb.

That makes sense because the sentence describes an ongoing or repeated situation:

• the dog is waiting
• the speaker gives the treat during that state

Imperfective is natural for:

• ongoing actions
• habitual actions
• background actions

So:

• czeka = waits / is waiting

A perfective form would not fit well here, because the focus is not on the waiting being completed, but on the dog being in that calm waiting state.