Najpierw zamiatam podłogę miotłą, a potem myję ją mopem.

Najpierw means first / at first, and potem means then / afterwards. Together, Najpierw ... a potem ... is a very natural way to show the order of actions:

• Najpierw = first
• a potem = and then / and afterwards

The a here is a conjunction linking the two parts of the sentence. It often sounds like and, though sometimes it has a slight contrastive feel, like and then.

So the structure is:

• Najpierw robię X.
• A potem robię Y.

Very common and natural in Polish.

Because Polish usually leaves out subject pronouns when they are obvious from the verb form.

• zamiatam = I sweep
• myję = I wash

The verb ending already tells you the subject is I, so ja is not necessary.

You could say:

• Ja najpierw zamiatam podłogę...

but that usually adds emphasis, as if you were contrasting yourself with someone else:

• Ja zamiatam, a ty myjesz.
  I sweep, and you wash.

So in a neutral sentence, leaving out ja is normal.

Because zamiatać is a verb whose 1st person singular present form is zamiatam.

Its present-tense pattern is:

• (ja) zamiatam = I sweep
• (ty) zamiatasz = you sweep
• (on/ona) zamiata = he/she sweeps

Not all Polish verbs form the present tense in exactly the same way, so this is something you learn with the verb.

The infinitive is zamiatać, but the I form becomes zamiatam.

Because podłoga is the direct object of the verb zamiatam.

In Polish, direct objects often go into the accusative case. Since podłoga is a feminine singular noun, its accusative form is:

• podłoga → nominative
• podłogę → accusative

So:

• Podłoga jest brudna. = The floor is dirty.
  Here podłoga is the subject.
• Zamiatam podłogę. = I sweep the floor.
  Here podłogę is the object.

This is one of the most important case patterns to learn.

Because Polish often expresses using a tool by putting the noun into the instrumental case, without needing a separate word for with.

So:

• miotła = broom
• miotłą = with a broom / using a broom

and

• mop = mop
• mopem = with a mop / using a mop

That means:

• zamiatam podłogę miotłą = I sweep the floor with a broom
• myję ją mopem = I wash it with a mop

This is very natural Polish. English uses a preposition; Polish often uses case instead.

Both words are in the instrumental case, but they belong to different noun types, so they take different endings.

• miotła is a feminine noun ending in -a

  • nominative: miotła
  • instrumental: miotłą

• mop is a masculine noun

  • nominative: mop
  • instrumental: mopem

So the difference is caused by gender and declension pattern, not by a difference in meaning.

Very roughly:

• many feminine nouns in -a → instrumental -ą
• many masculine/neuter nouns → instrumental -em

Ją means her or it in the accusative case. Here it means it, referring back to podłogę.

Since podłoga is a feminine noun, the pronoun must also be feminine:

• podłoga = floor
• ją = it (referring to a feminine noun)

So:

• myję ją mopem = I wash it with a mop

In English, it does not change for grammatical gender, but in Polish pronouns do.

Yes. You could say:

• Najpierw zamiatam podłogę miotłą, a potem myję podłogę mopem.

This is grammatically correct, but it sounds more repetitive. Using ją is more natural because the object has already been mentioned.

So Polish works like English here:

• I sweep the floor, and then I wash it.

instead of

• I sweep the floor, and then I wash the floor.

Polish word order is flexible, but some orders sound more natural than others.

In this sentence:

• myję ją mopem

the order is very natural:

• verb
• object pronoun
• instrument

You can sometimes move things around for emphasis, for example:

• Najpierw zamiatam podłogę miotłą, a potem ją myję mopem.

This also works, but it puts more focus on ją / the floor.

So yes, word order can change, but the original version is a normal neutral order.

Yes, both are present tense imperfective forms.

• zamiatać → imperfective → zamiatam
• myć → imperfective → myję

Imperfective is used for:

• habitual actions
• ongoing actions
• general descriptions
• sequences described in a neutral, non-completion-focused way

So the sentence can sound like:

• a routine: First I sweep the floor with a broom, then I wash it with a mop
• a description of what I am doing step by step

If you wanted to emphasize one completed future sequence, Polish would often use perfective verbs instead, for example:

• Najpierw zamiotę podłogę, a potem ją umyję.

That means more like:

• First I’ll sweep the floor, then I’ll wash it.

Because myć is an irregular or partly irregular-looking verb, and its 1st person singular present form is myję.

Some present forms are:

• (ja) myję = I wash
• (ty) myjesz = you wash
• (on/ona) myje = he/she washes

This is just the correct conjugation pattern for myć. It is a very common verb, so it is worth memorizing.

You can say just potem, and it is still correct:

• Najpierw zamiatam podłogę miotłą, potem myję ją mopem.

That sounds fine.

Adding a makes the link between the two actions a little smoother and more explicit:

• Najpierw ..., a potem ...

This is a very common paired structure in Polish, so learners will hear it often.

It can be understood either way, depending on context.

Because the verbs are imperfective present tense, the sentence may describe:

• a routine or usual method
  First I sweep the floor with a broom, then I wash it with a mop.

or

• what the speaker is doing now, in a kind of step-by-step description
  First I’m sweeping the floor with a broom, and then I’m washing it with a mop.

Polish present tense often covers both meanings, and context usually makes it clear.