maturi no yatai de takoyaki wo katte, tomodati to issyo ni tabemasita.

の links two nouns together. In this sentence, 祭りの屋台 means a festival stall or a food stall at a festival.

• 祭り = festival
• 屋台 = stall / stand
• 祭りの屋台 = the stall of the festival / a festival stall

This use of の is very common in Japanese. It often works like of, at, or an apostrophe-s in English, depending on the context.

で marks the place where an action happens.

So in 屋台でたこ焼きを買って, で shows that the buying happened at the stall.

Compare:

• 学校で勉強する = study at school
• 店で買う = buy something at a store

Here:

• 屋台で = at the stall

を marks the direct object of the verb—the thing that is bought, eaten, seen, etc.

In this sentence:

• たこ焼きを買って = bought takoyaki

So たこ焼き is the thing being bought.

Later, the same たこ焼き is also understood as the thing being eaten, even though を is not repeated before 食べました. Japanese often leaves out repeated information when it is clear from context.

買って is the て-form of 買う (to buy).

In this sentence, it connects two actions:

1. たこ焼きを買って = bought takoyaki
2. 友達と一緒に食べました = ate it together with a friend

So 買って works like and then bought / after buying / bought and.

This is a very common use of the て-form: linking actions in sequence.

When Japanese links actions with the て-form, usually the earlier verb takes て-form, and the final verb shows the main tense and politeness.

So:

• 買って = connecting form
• 食べました = final verb, showing polite past

This tells us the whole sentence is in the past and polite style:

• bought ... and ate

If both were in dictionary form, it would not connect properly in normal Japanese.

Japanese often omits the subject when it is obvious from context.

In English, you usually need to say I bought ... and ate ....
In Japanese, if it is already clear who did the action, the subject is often left out.

So this sentence naturally implies:

• I bought takoyaki at a festival stall and ate it together with a friend.

Omitting the subject is extremely common in Japanese.

友達と一緒に means together with a friend.

Breakdown:

• 友達 = friend
• と = with
• 一緒に = together

So:

• 友達と = with a friend
• 友達と一緒に = together with a friend

Using both gives a clear sense of doing the action together.

Yes, you could.

• 友達と食べました = I ate with a friend.
• 友達と一緒に食べました = I ate together with a friend.

The version with 一緒に emphasizes the idea of togetherness a bit more.
Without it, the sentence is still perfectly natural.

In 一緒に, the に turns 一緒 into an adverb-like expression, meaning together.

So:

• 一緒 = together / same / company
• 一緒に = together, in a way that describes how the action is done

It modifies the verb 食べました:

• 友達と一緒に食べました = ate together with a friend

This pattern is common with words that act like adverbial phrases.

Yes. That is understood automatically.

The sentence says:

• たこ焼きを買って = bought takoyaki
• 友達と一緒に食べました = ate together with a friend

Japanese often leaves out repeated objects when they are obvious. So the listener naturally understands:

• I bought takoyaki at a festival stall, and then ate it together with a friend.

You do not need to repeat たこ焼きを before 食べました unless you want extra clarity or emphasis.

Here are the common readings:

• 祭り = まつり
• 屋台 = やたい
• たこ焼き = たこやき
• 買って = かって
• 友達 = ともだち
• 一緒に = いっしょに
• 食べました = たべました

So the full sentence is read:

まつり の やたい で たこやき を かって、 ともだち と いっしょ に たべました。

食べました is polite past.

• 食べる = plain / dictionary form
• 食べた = plain past
• 食べます = polite non-past
• 食べました = polite past

Since the sentence ends with 食べました, the whole sentence is in polite style.
That is a very common style for textbook examples and everyday respectful conversation.

The comma mainly helps readability. It shows a pause between the two linked actions:

• 買って、
• 友達と一緒に食べました。

Japanese punctuation is often lighter and more flexible than English punctuation. The sentence would still be understandable without the comma, but including it makes it easier to read.