Demà em trobaré amb la meva amiga a la plaça després de la classe.

Because Catalan often uses the pronominal verb trobar-se amb to mean to meet someone / to meet up with someone.

So:

• trobar = to find
• trobar-se amb = to meet

The em is the weak pronoun that goes with jo (I). It is not translated literally in English here; it is just part of the verb pattern.

So em trobaré amb la meva amiga means I will meet my friend, not I will find myself with my friend.

Trobaré is the first-person singular simple future of trobar.

It means I will find or, in this sentence with em and amb, I will meet.

The future is often formed by adding endings to the infinitive:

• trobar
  • -é → trobaré = I will...
• trobaràs = you will...
• trobarà = he/she will...

So here em trobaré means I will meet.

This is a very common point of confusion.

• trobar usually means to find
  • Trobo les claus = I find the keys
• trobar-se amb means to meet or to run into
  • Em trobo amb la meva amiga = I meet my friend

So in your sentence, the meaning comes from the whole structure trobar-se amb, not just from trobar by itself.

Because the normal Catalan pattern here is trobar-se amb algú = to meet someone.

English says:

• I met my friend

Catalan usually says:

• Em vaig trobar amb la meva amiga
• Em trobaré amb la meva amiga

So amb is part of the usual construction after trobar-se.

Catalan normally uses the definite article before possessives:

• el meu amic = my friend
• la meva amiga = my friend
• el meu llibre = my book

This is different from English, where you usually say just my friend without the.

So la meva amiga is the normal Catalan way to say my friend.

Because the possessive has to agree with the noun in gender and number.

Amiga is:

• feminine
• singular

So the matching possessive is meva.

Compare:

• el meu amic = my male friend
• la meva amiga = my female friend
• les meves amigues = my female friends

The preposition a is commonly used for location or destination, often meaning at, to, or sometimes in, depending on context.

So:

• a la plaça = at the square / in the square

Also, this is a good place to notice contractions:

• a + el = al
• but a + la = a la (no contraction)

So:

• al parc = to the park
• a la plaça = to/at the square

Yes, plaça is related to plaza, but in Catalan it usually means a town square or public square.

So a la plaça usually means something like:

• at the square
• in the town square
• at the plaza

The exact English translation depends on context, but square is often the most natural choice.

Because després normally takes de before a noun.

So:

• després de la classe = after class
• després del dinar = after lunch
• després de la reunió = after the meeting

Think of després de as a fixed pattern meaning after when it is followed by a noun phrase.

Catalan often uses the definite article where English does not.

So English may say:

• after class
• after school
• after dinner

But Catalan often says:

• després de la classe
• després de l’escola
• després del sopar

In this sentence, la classe sounds like the class we both know about / the class on the schedule.

The word order can change. Catalan is fairly flexible, especially with time expressions and place phrases.

The original sentence:

• Demà em trobaré amb la meva amiga a la plaça després de la classe.

is perfectly natural, but you could also say:

• Em trobaré amb la meva amiga demà a la plaça després de la classe.
• Després de la classe, em trobaré amb la meva amiga a la plaça.
• A la plaça, demà em trobaré amb la meva amiga després de la classe.

Starting with Demà puts the focus on tomorrow.

The accent marks show where the stress falls.

• demà is stressed on the last syllable
• trobaré is also stressed on the last syllable

So roughly:

• de-MÀ
• tro-ba-RÉ

The accent can also help distinguish forms and make pronunciation clearer for learners.

It can, depending on context, because trobar-se amb can mean either:

• to meet
• to meet up with
• to run into

But in this sentence, the extra details demà, a la plaça, and després de la classe make it sound more like a planned meeting:

• Tomorrow I’ll meet my friend in the square after class.

So here the most natural interpretation is probably a planned arrangement.