Welcome to FM, Marina! I hope you find the help you need here.
Two books I found helpful years ago (and still reread periodically) are Orson Scott Card's
How to Write Science Fiction and Fantasy and
Characters and Viewpoint. They're both easy to read, explain things clearly, and aren't so clouded with lesson-bits they may block a writer (for
me, I find the more involved stuff nowadays blocks my creative juices as I try to consciously figure out how to implement them--these two books don't do that). They're good books to have handy. (I linked to the versions of the books I have, but there are cheaper ones available--just do a title+author search.)
Also, for the nuts-and-bolts of writing fiction (or anything really, but especially fiction), I find Strunk & White's
Elements of Style a nice go-to for answering grammar and other questions. (I have this in a nookbook.)
And, as always, a dictionary is good. I have a Mirriam-Webster unabridged print dictionary as well as use a variety of online dicitonaries:
Mirriam-Webster Online - for lookups when I'm in the middle of writing a scene and don't want to step away for my print dictionary.
Thesaurus.com - For finding just the right word to replace redundancies in edits.
Urban Dictionary - For finding a definition of a modern word I don't want to use in my own fantasy/science-fantsy writing so I can hopefully find a way to describe something I only have the modern-day term for.
As for where to begin with writing a fantasy novel, I suggest since you seem like you're new to it, you begin with what you already have in mind and explore and experiment from there. One of the best things about writing fantasy is that the writer gets to do a wide variety of things and each writer begins in a different place with their stories. If you have world building knowledge (facts about the fantasy world you want to write in), write them down. If you have a timeline for some events for the world/country or even a character, write them on a timeline, either on paper by hand, or on computer (one program I've found
extremely useful for timelining things is
Aeon Timeline). If you want to know what the lay of the land is, or just have ideas for cities and geography, draw a map. If a couple characters are talking at you, write character descriptions and see if you can niggle motivations and some plot points out of them while you're at it.
As you write more, you'll get to know your writing habits better.