Opening Repertoire the Modern Defence
https://www.newinchess.com/media/wysiwyg/product_pdf/8213.pdf
Modern defence

The DVD from Hillarp Persson & Williams from GingerGM is excellent.
It gives you a lot of ideas how to play this opening, how te meet h4 (very important!). It will get you started and after that you can dig in with some book study

Numerous books out there. In addition to the ones mention:
Modern Defense: Move by Move (Lakdawala)
I think Seiriwan and someone else wrote the 3 book series - Chess on the Edge, which is roughly 700 annotated games of Duncan Suttles, a Canadian GM. Roughly half of the games have him playing Black, and of those, literally over 98 percent of them are the Modern Defense, both against e4 and d4.
I like to play modern defense but I've got some problems to study it, does someone knows it and could help me?