Najpierw kończę listę zadań, a potem sprawdzam listę gości na niedzielny obiad.

They mark the sequence very clearly:

• najpierw = first
• potem = then / afterwards

So Najpierw..., a potem... is a very common Polish pattern meaning First..., and then...

You could sometimes omit one of them if the order is obvious, but using both sounds natural and helps organize the sentence clearly.

In this sentence, a links two actions in a mild contrast or sequence:

• Najpierw kończę listę zadań, a potem sprawdzam...

Here a works a bit like and then / while on the other hand / and after that.

If you used i, it would simply join the two actions as and:

• Najpierw kończę listę zadań i potem sprawdzam...

That is understandable, but a potem is the more natural combination when moving from one step to the next.

Polish often uses the present tense to describe:

• a habitual routine
• a planned sequence
• a step-by-step description of what someone does

So Najpierw kończę..., a potem sprawdzam... can mean something like:

• First I finish..., then I check...
• What I do is: first I finish..., then I check...

This does not have to mean the action is happening literally at this exact second. It can describe a normal order of actions.

Kończyć is the imperfective verb, and skończyć is the perfective partner.

Here:

• kończę = I am finishing / I finish
• skończę = I will finish

In Polish, a perfective verb usually does not have a present meaning. Its present-looking forms normally refer to the future.

So:

• Najpierw kończę listę zadań... = natural for describing a routine or sequence
• Najpierw skończę listę zadań... = First I’ll finish the task list...

That would shift the meaning toward the future.

Because kończyć takes a direct object, and direct objects are often in the accusative case.

The basic noun is:

• lista = list

But after kończę it becomes:

• listę = accusative singular

So:

• kończę listę = I finish the list

This is a very common feminine noun pattern:

• nominative: lista
• accusative: listę

Because in listę zadań, the second noun means of tasks.

This is a noun + noun structure:

• lista zadań = list of tasks

In Polish, after nouns like lista, the thing listed is often put in the genitive case.

So:

• zadania = nominative plural, tasks
• zadań = genitive plural, of tasks

That is why:

• lista zadań = task list
• listę zadań = task list in the accusative as the object of the verb

Here gości is best understood as genitive plural: of guests.

So:

• lista gości = guest list literally list of guests
• listę gości = accusative list
  • genitive of guests

This is parallel to:

• lista zadań = list of tasks

It can be confusing because gości can also look like other case forms, but in this phrase the structure is:

• listę = the direct object
• gości = dependent noun meaning of guests

It means for Sunday dinner / for a Sunday lunch.

Breakdown:

• na = here it means something like for
• niedzielny = Sunday / Sunday-related
• obiad = a main meal, often translated as lunch or dinner depending on context

So lista gości na niedzielny obiad means:

• the guest list for Sunday dinner
• or the guest list for Sunday lunch

The exact English meal word depends on context and family habits.

Both are possible, but they mean things slightly differently.

• niedzielny obiad = Sunday dinner/lunch, an adjective-based phrase
• obiad w niedzielę = dinner/lunch on Sunday, a prepositional phrase

In your sentence, niedzielny obiad sounds compact and natural, especially because it modifies the guest list:

• lista gości na niedzielny obiad = guest list for Sunday dinner

It is similar to English using an adjective in phrases like Sunday lunch.

Yes, Polish word order is fairly flexible, but not all versions sound equally natural.

The given sentence is very natural because it presents the order clearly:

• Najpierw kończę listę zadań, a potem sprawdzam listę gości na niedzielny obiad.

You could also say, for example:

• Kończę najpierw listę zadań, a potem sprawdzam listę gości na niedzielny obiad.

That is still understandable, but it sounds a bit less neutral. Putting najpierw at the beginning is the most straightforward choice.

Yes, sometimes, but the sentence would lose some of its clear step-by-step feeling.

For example:

• Kończę listę zadań, a potem sprawdzam listę gości...
• Najpierw kończę listę zadań, a sprawdzam listę gości... — this version is not good, because a alone does not express then strongly enough here

The most natural full version is:

• Najpierw..., a potem...

That pair is very common and idiomatic.

A rough pronunciation guide is:

• kończę ≈ KON-cheh, but with a nasal sound in koń

More carefully:

• ń is like a soft ny sound
• cz sounds like ch in chop
• ę at the end is often pronounced approximately like e or a nasalized e, depending on speech style

So for many learners, a useful first approximation is:

• kończę ≈ KON-che

But if you want to sound more Polish, try to keep the soft ń and a slight nasal quality before cz.

It most often means check or verify.

So here:

• sprawdzam listę gości = I check the guest list

It suggests you are reviewing it to make sure it is correct, complete, or up to date.

If you only wanted to say I look at the guest list, Polish might use a different verb, such as patrzę na in some contexts. Sprawdzam is more purposeful than just looking.