Once you've downloaded a crate, here's how to get those tracks into your DJ software.
A downloaded crate lands on your device as a zip file.
Find the zip in wherever your browser saves downloads, then open it to unzip — you'll see all the MP3s inside.
Drag those files into a folder on your device (or drop them straight onto your software's library).
Open your DJ software — Serato, Rekordbox, Traktor, whatever you run — and drag the folder in. They're standard MP3s, so they import like any other tracks.