You use it before the game begins. After you put the
Brainstorm into your hand, you’ll shuffle the rest of your deck. Then you’ll draw the normal 3 cards at the start of the game. This means you’ll start the game with 4 cards in hand (Brainstorm plus the 3 you draw). You’ll still draw a card at the start of your first turn.
Can this ability trigger more than once in a the same turn?
[Source: WotC]
No. You play your third action in a turn only once.
I have a team of all Autobots, including Captain Wheeljack in bot mode. I play
Brainstorm, and as the first action, play
Confidence. Do I play my second action for Brainstorm now, or do I resolve Confidence first and play an action via Confidence? Either way, this will trigger Captain Wheeljack’s "When you play your third action" ability. Do I draw the card for that immediately, or do I wait until all the actions played via Confidence and Brainstorm have resolved?
[Source: WotC]
Finish
Confidence first (including possibly playing another action), then play your second action for
Brainstorm. After that’s done, all abilities that triggered while Brainstorm was resolving happen in an order of your choosing.
Sure does.