You do not have to place a comma after the word "English". And the definite article "the" should replace the indefinite article "a".

Below I will place the above corrections to your entry in red and bold letters. This (_) indicates space.

I'd like to learn English_because it will help me in my future job.
I speak only Russian and I grew up in Russia.
I like reading, listening to music and I like to go to the gym.

As you can see, you did very good! Keep working hard on your English studies and you'll be great! Even as you see now, your writing skills for English are wonderful! I'm impressed! Keep up the good work!

First notebook entry: Introducing myself

I'd like to learn English, because it will help me in my future job.
I speak only Russian and I grew up in Russia.
I like reading, listening to music and I like to go to a gym.

Отлично !!