In Japanese, します is used for the simple present tense but sometimes it's used for future tense depends on the context. しています is literally means "be + ing" but it's also used for "I'm in the situation of doing ... ", in this case, learning Japanese. So, saying 日本語を勉強しています[にほんごをべんきょうしています] is very natural to us if you started studying Japanese and 日本語を勉強します[にほんごをべんきょうします] generally sounds "I will study Japanese" to us. I hope this was helpful.

します 現在形　習慣を表す shimasu means present tense or use for habit 私は放課後テニスをします。 I play tennis after school. しています 現在進行形 verb+ing 私は今映画を見ています。 I'm watching a movie now I hope this helped you.

I study Japanese. I am studying Japanese.

I do study japanese I am studying japanese right now