1 You forgot the letter S in &with_genres

I get 20 movies but none of them has genre...

2 You actually got 405979 movies with this wrong search.
See the beginning of the answer the following information:

page    1
total_results   405979
total_pages 20299

There are 20 movies per page. And you got 20299 pages.
You can add the &page parameter in your Request.
https://api.themoviedb.org/3/discover/movie?api_key=[MY_KEY]&language=en-US&page=1&with_genres=10749

... but is it possible to give a range of year.

3 If this is a question, the answer is yes.
I suggest you carefully read the instructions on this page:
https://developers.themoviedb.org/3/discover/movie-discover
To set a Range of dates, you need to use the parameters:
primary_release_date.gte = equal to or greater than
primary_release_date.lte = equal to or less than

https://api.themoviedb.org/3/discover/movie?api_key=[MY_KEY]&language=en-US&page=1&primary_release_date.gte=2012-04-25&primary_release_date.lte=2017-12-23&with_genres=10749
The answer will be with this quantity:

page    1
total_results   5166
total_pages 259

Thanks for prompt response :)

Hey! I Have a question. Is it possible to give a range of vote_average?

The solution is the same, but with the voting parameters:
vote_average.gte
vote_average.lte

See here: https://developers.themoviedb.org/3/discover/movie-discover

Thanks a lot!