zyugyou ga owattara, ie ni modoru mae ni tomodati wo kafe ni sasou tumori da.

Because the ~たら conditional attaches to the past plain form of a verb.

So:

• 終わる = to end
• 終わった = ended
• 終わったら = when/after it ends

Even though it looks like a past form, ~たら often refers to a future sequence in sentences like this. It means something like once class is over or when class ends.

This part is a time/condition clause.

• 授業 = class, lesson
• が = marks 授業 as the subject of 終わる
• 終わったら = when/after it ends

So 授業が終わったら literally means when class has ended or once class is over.

The clause sets up the timing for the main action later in the sentence.

が marks 授業 as the subject of 終わる: the class is what ends.

So:

• 授業が終わる = the class ends

If you used は, it would sound more like you were making 授業 the topic, possibly with contrast or emphasis depending on context. In a straightforward sentence like this, が is the natural choice.

Because 前に normally follows the dictionary form of a verb when you mean before doing something.

So:

• 戻る前に = before returning
• 食べる前に = before eating
• 寝る前に = before sleeping

By contrast, 後で / 後に often comes after a past form:

• 戻った後で = after returning

So in this sentence, 家に戻る前に correctly means before going back home.

It modifies the main action 誘う.

So the order of events is:

1. class ends
2. before going home
3. invite a friend to a café

In other words, the inviting happens before going home.

They are doing two different jobs:

• 家に戻る: に marks the destination of 戻る
  → return home
• カフェに誘う: に marks the place you are inviting someone to
  → invite someone to a café

So even though the same particle appears twice, its role depends on the verb it goes with.

Because with 誘う, the person being invited is the direct object.

So:

• 友達を誘う = invite a friend
• 友達をカフェに誘う = invite a friend to a café

A helpful way to think of it is:

• を = the person you invite
• に = the place you invite them to

Because 誘う often uses に for the destination/place someone is invited to.

• カフェに誘う = invite someone to a café

If you used で, it would sound more like the café is the location where the act of inviting happens, not the place you are inviting them to. That is not the intended meaning here.

つもりだ expresses intention or plan.

• 誘う = invite
• 誘うつもりだ = I intend to invite / I plan to invite

So the sentence is not just describing an action; it is expressing the speaker’s plan.

It is a common pattern:

• 行くつもりだ = I intend to go
• 勉強するつもりだ = I intend to study

Yes. Japanese often omits subjects when they are understood from context.

Because of つもりだ, the natural understanding is that the speaker is talking about their own intention:

• (I) intend to invite a friend...

If needed, Japanese could say 私は, but it is usually unnecessary here.

Yes. 友達 by itself does not clearly mark singular vs. plural.

So it could mean:

• a friend
• friends

The exact meaning depends on context. In many textbook-style translations, it is often rendered as a friend, but Japanese itself is less explicit here.

Yes, to some extent. Japanese is flexible as long as the grammar makes the relationships clear.

For example, the time-related parts often come before the main verb, which is what happens here:

• 授業が終わったら、家に戻る前に、友達をカフェに誘うつもりだ。

This is natural because Japanese commonly places background information first and the main action near the end.

A useful breakdown is:

• 授業が終わったら = when class ends
• 家に戻る前に = before going home
• 友達をカフェに誘う = invite a friend to a café
• つもりだ = intend to

So the sentence is built like this:

[When class ends], [before going home], [I intend to invite a friend to a café].

That kind of time/background information first, main statement last structure is very common in Japanese.