After you’ve created an account, you can favorite tracks to quickly save them for later or add them to your collections.
To favorite a track: click on the star-symbol in the track player.
To add a track to your collections: click on the plus icon in the track player. You can choose to add the track to a previously created collection or to create a new collection to add the track to.
You can find your created collections, or create a new one, under "Your Collections".
You can find out more about collections here.
All your downloaded tracks are automatically saved to "Downloads", which can be found under "Your Library" or in the drop down menu.