Po lekcji spotkamy się u nas, ale najpierw muszę się wylogować z konta w pracy.

Because the preposition po often requires the locative case when it means after in time expressions.

• lekcja = lesson
• locative singular: lekcji

So:

• po lekcji = after the lesson

This is a very common pattern:

• po pracy = after work
• po obiedzie = after lunch
• po spotkaniu = after the meeting

So the form lekcji is there because of the preposition po.

Spotkać się is a reflexive verb meaning to meet in the sense of meet each other / get together.

So:

• spotkać = to meet someone
• spotkać się = to meet up, to meet each other

In this sentence, spotkamy się means we will meet up.

The się is part of the verb, not a separate word with a literal meaning like ourselves in English. In many Polish verbs, się is simply required.

Compare:

• Spotkałem Marka. = I met Marek.
• Spotkaliśmy się z Markiem. = We met up with Marek.

Because spotkać is a perfective verb, and perfective verbs do not have a present tense meaning. Their present-looking forms refer to the future.

So:

• spotkamy się literally looks like a present-tense form
• but because spotkać się is perfective, it means we will meet

This is normal in Polish:

• zrobię = I will do
• napiszesz = you will write
• wyjdziemy = we will go out

If you wanted a true present meaning, you would use an imperfective verb, but here the future is the natural choice.

U nas is a very natural Polish way to say at our place.

The preposition u is commonly used when talking about being at someone's home, office, place, or location associated with a person.

• u mnie = at my place
• u ciebie = at your place
• u nas = at our place
• u rodziców = at my parents' place

So spotkamy się u nas means we’ll meet at our place.

It is shorter and more idiomatic than w naszym domu, which would sound more literal: in our house/home.

Because u requires the genitive case.

The basic pronoun is:

• my = we

But after u, you need the genitive form:

• nas

So:

• u nas = at our place / with us

The same happens with other pronouns:

• u mnie = at my place
• u ciebie = at your place
• u niego = at his place

Because there are two different verbs that require się:

• spotkać się = to meet up
• wylogować się = to log out

So each verb keeps its own się:

• spotkamy się
• muszę się wylogować

This is completely normal. The się belongs to the verb it goes with.

Muszę się wylogować means I have to log out.

This structure is:

• muszę = I must / I have to
• wylogować się = to log out

So together: I have to log out

If you said wylogowuję się, that would mean I am logging out or I log out, not I have to log out.

The sentence is expressing obligation first, so the modal verb musieć is needed.

After modal verbs like musieć (must / have to), Polish normally uses the infinitive.

So:

• muszę pracować = I have to work
• muszę iść = I have to go
• muszę się wylogować = I have to log out

That is the standard structure:

muszę + infinitive

Wylogować się is the perfective form, meaning a single completed action: to log out.

That fits well here, because the speaker means one completed action that must happen before the meeting.

• muszę się wylogować = I need to log out

The imperfective wylogowywać się usually refers to repeated, habitual, or ongoing action, and is much less likely here.

So the perfective form is the natural choice because the speaker wants to complete that action first.

Because the preposition z here means from / out of, and it requires the genitive case.

• konto = account
• genitive singular: konta

So:

• z konta = from the account / out of the account

In computer-related Polish, wylogować się z konta is the normal expression for to log out of an account.

Konta is the genitive singular form of konto.

Dictionary form:

• konto = account

After z in this meaning, Polish uses the genitive:

• z konta = from the account

This kind of change is very common after prepositions.

Because w meaning in / at usually requires the locative case when talking about location.

• praca = work
• locative singular: pracy

So:

• w pracy = at work / in the workplace

This is a fixed and very common phrase.

Compare:

• w domu = at home
• w szkole = at school
• w biurze = in the office

Because the two actions happen at different times.

• spotkamy się = we will meet up later
• muszę się wylogować = I have to log out first

So the meeting is in the future, but the obligation exists now, before that future event.

That is completely natural in both Polish and English:

• We’ll meet later, but first I have to log out.

Najpierw means first or first of all, and here it introduces the action that must happen before the meeting.

• ale najpierw muszę się wylogować... = but first I have to log out...

Its position is very natural: it comes early in the clause to highlight the sequence of events.

You could move it in some contexts, but this placement is the most neutral and common.

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

The original sentence:

• Po lekcji spotkamy się u nas, ale najpierw muszę się wylogować z konta w pracy.

is very natural and neutral.

You can move elements for emphasis, for example:

• Po lekcji u nas się spotkamy...
  This is possible, but less neutral and more marked.

• Najpierw muszę się wylogować z konta w pracy...
  This puts stronger emphasis on first

Polish often changes word order to shift emphasis, but the original order is probably the best one for everyday speech.

Literally, w pracy means at work / in work, not from work.

In this sentence, z konta w pracy most naturally means:

• out of the account at work
• or from my work account, depending on context

So w pracy describes the account or the location connected to logging out.

If Polish wanted to say from work more directly, it would usually use z pracy.

Compare:

• jestem w pracy = I am at work
• wracam z pracy = I’m coming back from work

Not exactly, though they can be similar depending on context.

• z konta w pracy = from the account at work / at the workplace
• z konta służbowego = from the work account / company account

Służbowy specifically means something like official, business, or work-related.

So if you want to emphasize that it is a company or job-related account, konto służbowe is more precise. The original sentence is a bit broader and more conversational.