How to learn Bengali?

[Moshin]

Hey guys,
im currently taking Bengali as one of my subjects for GCSEs,
but now i am finding it very difficult to learn the subject,
I mainly speak english to my friends, and I only speak
bengali to my family, the one thing I find difficult to learn is shuddo Bangla,
When I speak to my parents I speak Sylheti Bangla, so shuddo Bangla is like
a whole new language for me, because there is so much difference and so
many new words of which I dont understand, plus I mainly speak English,
I tried watching Bangla natoks n news to learn the flow of Bangla, but
still it's not working, is there any good advice that you can give me on how
to learn shuddo Bangla compared with Sylheti Bangla, or I'm done for!
So please give advice to me, accha tumrar bala takho.