@ele I mean vowels – it most usefull letters (its 6 only), then consonants
2) voiced and unvoiced letters
3) stress and intonation
My mother teaching Russian language in China in university. Its how she start her first lesson for students.
Russian some hard when learn it with books. I was in China last summer, her students talk
You can try this http://www.ph4s.ru/books/guman/rus/Russkiy_s_azov.rar
Its “Rusian from scratch”, on EN. Book in DJVU, need WinDjView reader
You can think about a language trip to Russia. Of course, online learning is a good way too, but only after you get to Russia you may experience the full immersion. Felix said talking to natives is very important: https://enjoyrussian.com/felix-about-russia-2/