Learn Hardcore Japanese: syuumatu ni watasi ha tomodati to issyo ni kantanna ryouri wo tukurimasu. - I make simple dishes together with a friend on the weekend.

You could also say 週末は to make “weekends” the topic (“As for weekends, I …”), which slightly changes the nuance to emphasizing weekends compared to other times.
週末に is a neutral way to say when the action happens.

Can the word order change? For example, can I say 私は週末に友達と一緒に簡単な料理を作ります?

Yes. Japanese word order is quite flexible as long as you keep the verb at the end and the particles attached to the right words.

All of these are natural (with slightly different emphasis):

週末に私は友達と一緒に簡単な料理を作ります。
私は週末に友達と一緒に簡単な料理を作ります。
友達と一緒に私は週末に簡単な料理を作ります。

English relies on word order; Japanese relies more on particles (は, に, と, を, etc.) to show each word’s role.

What is the difference between は in 私は and が? Could I say 私が here?

In this sentence, 私は marks “I” as the topic: what you are talking about is “me / my actions.”
が often marks the grammatical subject, especially when introducing new information or emphasizing “who” did it.

私は週末に料理を作ります。 – As for me, I cook on weekends. (Neutral/self-introduction style)
私が週末に料理を作ります。 – I (not someone else) will cook on the weekend. (Emphasis or contrast)

You can say 私が but it sounds like you’re stressing that you, specifically, are the one who cooks (e.g., in contrast to someone else).

Why is there と after 友達? I thought と means “and.”

と does mean “and” when joining nouns, but after a person’s noun it can also mean “with.”

友達と行きます。 – I will go with a friend.
母と父 – mother and father.

In this sentence, 友達と means “with my friend(s).”
So 友達と一緒に is literally “together with friend(s).”

Do I really need both と and 一緒に to say “with my friends”? What is the nuance?

You don’t have to use both; each has a slightly different role:

友達と行きます。 – I’ll go with my friend(s).
友達と一緒に行きます。 – I’ll go together with my friend(s). (Feels a bit more “togetherness” / doing it as a group.)

In your sentence:

友達と = “with (my) friend(s)”
一緒に = “together”

They’re often used together for a natural, friendly tone. But saying just 友達と簡単な料理を作ります is also grammatically correct.

What is 一緒に exactly, and where does it go in the sentence?

一緒に (いっしょに) is an adverb meaning “together”.

It usually goes before the verb (or close to the verb phrase):

友達と一緒に行きます。 – I will go together with my friend.
家族と一緒に住んでいます。 – I live together with my family.

In this sentence, it modifies 作ります, so 友達と一緒に簡単な料理を作ります = “(I) make simple dishes together with (my) friend(s).”

Why does 簡単 become 簡単な before 料理?

簡単 (かんたん) is a na-adjective (な-adjective).
When a na-adjective directly modifies a noun, you usually add な:

簡単な料理 – simple / easy dishes
静かな部屋 – a quiet room

When you use it as “is easy / is simple”, you don’t need な:

この料理は簡単です。 – This dish is simple.

So 簡単な料理 literally means “simple-type cooking,” i.e., “simple dishes.”

What is the role of を with 料理?

を marks the direct object of the verb – the thing that the action is done to.

本を読みます。 – I read a book.
水を飲みます。 – I drink water.

In this sentence:

料理 = cooking / dish(es)
料理を作ります = “make cooking/dishes” → “cook / make dishes”

So を shows that 料理 is what is being made.

Why is 作ります in the present tense when the meaning can be “I will cook” or “I usually cook”?

Japanese uses the non-past form (dictionary / polite present) for both present and future meaning, and also for habitual actions.

作ります can mean:

I cook / I make (habitually, generally)
I will cook / I am going to cook (future)

Context decides which is intended.
Because you have 週末に, it’s natural to understand it as a regular habit: “On weekends, I (usually) make simple dishes with my friends.”

Does 週末 mean “this weekend,” “the weekend,” or “weekends” in general? There is no plural marker.

Japanese usually doesn’t mark plural on nouns. 週末 can mean:

“this/that weekend” (specific)
“the weekend” (upcoming/mentioned)
“weekends” (in general, habitually)

Context gives the nuance.
With the non-past 作ります and no extra word like この, it most naturally reads as “on weekends (in general)” or “on the weekend” as a general habit.

If you want to be specific:

この週末に – this weekend
先週末に – last weekend
毎週末に – every weekend

Do I have to say 私? Can I drop it?

You can almost always drop 私 (and other pronouns) in Japanese when it’s clear from context who the subject is.

週末に友達と一緒に簡単な料理を作ります。
Still naturally means “I (will) make simple dishes with my friends on the weekend.”

Pronouns like 私 are often used when:

You want to explicitly introduce yourself.
There might be confusion about who is doing the action.
You want to contrast with someone else (e.g., 私は, “as for me”).

In everyday conversation, leaving out 私 sounds more natural if the subject is obvious.

Could I say 料理します instead of 料理を作ります? What’s the difference?

You sometimes see 料理します, but the more common and natural expression is:

料理を作ります
or 料理します in the sense of “I cook” (as an activity).

Nuance:

料理を作ります – literally “make dishes,” very natural for “cook (food).”
料理します – “do cooking / do cuisine,” sounds a bit more like talking about the activity of cooking.

In casual speech, people often just say:

週末は友達と簡単な料理を作る。 – On weekends I cook simple dishes with my friends.

What is the politeness level of 作ります, and how would the casual version of the sentence look?

作ります is the polite -ます form, used in most conversations with people who are not close friends or family, or in formal situations.

The casual (plain) form is 作る.
A natural casual version of the whole sentence is:

週末に友達と一緒に簡単な料理を作る。

You could also add だよ / よ etc. for friendly nuance in speech:

週末に友達と一緒に簡単な料理を作るよ。