Learn Swedish: Han dricker mycket kaffe eftersom han vill vara bra på att fokusera. - He drinks a lot of coffee because he wants to be good at focusing.

Kaffe is an uncountable mass noun. When you talk about drinking a substance in a general sense, Swedish uses the zero article (no article at all), just like English. You only use kaffet when talking about a specific coffee.

Why use mycket here instead of många?

Mycket means 'much' or 'a lot of,' and it is used with uncountable mass nouns like kaffe. You would only use många (many) for things you can count, like många koppar kaffe (many cups of coffee).

The English translation says 'at focusing,' so why does the Swedish sentence use att fokusera (to focus)?

Swedish doesn't have an '-ing' verb form that acts like a noun. Instead, when a verb follows a preposition like på, Swedish uses att plus the infinitive verb. So 'good at focusing' translates literally to 'good at to focus' (bra på att fokusera).

Why is the word order eftersom han vill vara and not eftersom vill han vara?

The word eftersom (because) starts a subordinate clause. These clauses always use straight Subject-Verb word order (han vill). The famous V2 rule (where the verb comes before the subject) only applies to main clauses, not subordinate clauses like this one.