Hi there! To write fantasy you need first to have read a lot of fantasy (not necessarily in English, as I think you're saying English isn't your first language).
I think, then, maybe creative writing classes - if you've never written fiction before - might be the way to go, rather than just picking up a How-To-Write-Fiction sort of instructional book.
Final thought - if you've never written fiction, and you're not 100% confident in your English, I wonder if you have considered writing fiction in your original language? I'm not really a writer, and others might know better (or advise different tactics), but it seems nowadays that there must be a market for good fiction in any language. So my thought is, develop your fiction-writing skills in your first language - learn how to write fiction over time, with study and practice and guidance - see what the market is like for stories written in your first language, and then once you have developed proficiency, attempt the English-language market* for your stories. Just my 2 cents. Best of luck in your journey, CC
*sorry, that's assuming your intention is to, one day, publish in English; I may have misunderstood your first post.