Crates are a great way to organize music you like on the site. To add a song to your crate, just click the Crates button on a track, which looks like a box.
When you click that button, a pop-up will appear where you can add the track to an existing crate or create a new one.
To access the crates you've made, click the Crates link under the Record Pool menu on the left. There, you'll see a tab that says My Crates.