Learn Hardcore Japanese: watasi ha syuumatu ni resutoran wo yoyakusimasu. - I will make a reservation at a restaurant on the weekend.

は is the topic marker, which introduces what you’re talking about (“As for me…”). が is the subject marker, often used to present new information or emphasize the subject (“It’s me who will…”). In a plain statement like this, you normally use 私は to set “I” as the topic. If you said 私が週末に…, it would sound more like you’re contrasting “me” against someone else.

What does に after 週末 do? Can I omit it or replace it with は?

に marks a specific point in time, similar to “on” in English: “on the weekend.”
You can sometimes drop に in casual speech: “週末、レストランを予約します” with just a comma.
If you replace に with は (“週末はレストランを予約します”), you make 週末 the topic and imply a habitual or general action (“As for weekends, I make restaurant reservations,” suggesting you do this every weekend).

Why is レストラン written in katakana instead of hiragana or kanji?

レストラン is a loanword from English (restaurant), and Japanese conventionally writes foreign words in katakana. Hiragana is reserved for native words and grammatical elements, while kanji are used for Chinese-origin or native content words.

Why is を used after レストラン? Isn’t 予約 the verb?

予約する is a suru-verb, formed by the noun 予約 plus the verb する. In レストランを予約します, the entire verb is 予約します, so レストラン is the direct object of that action and takes を. You’re literally saying “reserve the restaurant.”

What tense is 予約します? How do I say “I will reserve”?

Japanese ～ます form doesn’t distinguish present from future tense by conjugation. 予約します can mean “I reserve” or “I will reserve,” depending on context. Here, because you mention 週末に (a future time), listeners understand it as “I will reserve.”

Could I say 予約する instead of 予約します?

Yes. 予約する is the plain/dictionary form (“to reserve”), and 予約します is the polite form. In informal situations you might drop ます and say “週末にレストランを予約する.”

Can I drop 私は and just say 週末にレストランを予約します?

Absolutely. Japanese often omits the topic/subject when it’s clear from context. If nobody is confused about who’s doing the action, you can leave out 私は.

Why does the verb come at the end? Do all Japanese sentences end with a verb?

Standard Japanese word order is Subject–Object–Verb (SOV), so the main verb usually appears at the end. While some sentences end with です, だ, or even adjectives, the core verb of the clause normally goes last.

Could I say レストランの予約をします instead of レストランを予約します?

Yes. In レストランの予約をします, you treat 予約 as a noun (“a reservation”) and use の to link it to レストラン (“reservation of a restaurant”), then を marks that noun as the object of します. Both that and レストランを予約します convey “make a restaurant reservation.”