To purchase one, just select the amount and continue through check-out. It will appear in *your* account after your payment has been processed. Then you simply log into your account and choose what you want to do with it :) You can keep it, split it up or send it to a friend! If you or they do not use the full amount on a purchase, the balance remains in your/ their account for your future use.
If you would like to have one mailed to you or a friend, simply make a note of that in the comments box during checkout. Be sure to provide the mailing address and recipient's name!