Go to the "My Team" tab, then go do "Manage DL", and then there should be a tab next to your DL eligible player that says "To DL". There's only one spot on the DL, so you can't put Cabrera on the DL if someone on your roster is already there. You'd do the same thing to activate the player when he cmes off the DL by clicking on "activate". It's as easy as it sounds.