Я оставил заявку на курс русского языка.

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Breakdown of Я оставил заявку на курс русского языка.

• на: for
• русский: Russian
• язык: the language

Questions & Answers about Я оставил заявку на курс русского языка.

Why is оставил used here if I learned it means left?

Yes, оставить often means to leave something somewhere, but in some contexts it also means to leave behind / submit / provide.

In оставил заявку, the idea is I left/submitted an application. This is a normal Russian way to say that someone filled in or sent in a request/application, especially online or by phone.

So here оставил заявку is best understood as submitted an application / left a request.

Why does оставил end in -л?

That is the marker of the past tense in Russian.

The infinitive is оставить.
To form the past tense, Russian usually replaces -ть with -л:

• оставить → оставил = left / submitted
• делать → делал = did / was doing

In this sentence, оставил means submitted / left in the past.

Why is it оставил and not оставила?