How can I give away a humble bundle?

Search in the games list for 'Humble'; most (if not all) of the Humble Bundles are listed their under their given name (i.e. Humble Indie Bundle 4).

i think you have to select gift when you buy it, then it emails the whole bundle to someone instead of just individual games

You can ask support to add it to giveaway list.

Another simpler way to do it is to select one of the games in the bundle to give away, and then in the description say you'll be giving away the whole bundle.