Press and pinch. That's all there is to it. Press and pinch.

I once got into a discussion about bras while sitting with a bunch of friends at a restaurant. I said that they weren't all that difficult to operate...and so to illustrate, I put my hand on my female friend's back, and through two layers of clothing (one of which was a fleece) undid her bra. Pop. Just like that.

(She spent the next two minutes swearing at me and trying to redo her clasp through her clothing. That's MUCH harder.)

It's like button-fly jeans. Once you get used to opening them, they're a cinch.