Go to 'My Library' in the top right part of your screen.
Click on the 'Playlist' tab
Click 'Create Playlist'
Name your playlist then click 'Add Tracks'
You can then choose between tracks you have already purchased in 'Collection' or go to 'All Tracks' to choose from the Beatport catalog
Click the check box on the right side next to each track you wish to add to your playlist and click 'Done' when all tracks are added
Click 'Save Changes'
You can then see your newly created playlist under the 'Playlists' tab