You can buy a gift bundle by selecting the "Make a gift" option on the purchase form when you're buying a bundle.
Check the option, and enter the email address of the person you want to send the bundle to. If you don't know who to send it to yet, you can hold on to it by entering your own email address. Gifted bundles will be available under the "Gifted bundles" tab on your purchases page. It will show you who you've sent gift bundle to, and whether or not they redeemed it. If the gift hasn't been redeemed, you will see a link to the gift redeem page that you can send to someone else.
If you forgot to mark an order as a gift when purchasing, you can mark it afterwards by expanding the bundle on your purchases page and clicking on the "gift" button. The bundle will be available in your "Giveaway" tab. Please see the article on giveaway on how to gift a bundle marked this way.