Choice, it all depends on how agile your craft is. Thunderhawks are flying barns and have a low agility, so they can only use manoeuvre cards that are classed as low. My Thunderbolts are classed as having a high agility, so they can perform both low and high manoeuvres. My pal's Eldar Nightwings are classed as very high on their agility, so they can perform all manoeuvres, from low to very high.
The cards will tell you all you need to know:
- where you end with your manoeuvre
- your altitude and speed at the end of the manoeuvre (for example if you perform a power dive you lose D3+1 altitude but gain +2 speed. When you climb you can gain 1/2 altitude but also lose 1/2 speed depending on how high you climb)
And then you can perform your manoeuvres as many times as you want. You can for example perform a power dive in turn 1 and 2, perform a high-G turn on turn 3 and a half loop on turn 4. Just don't forget to shoot at the enemy when you cross sights
sweatdrop 
It's kinda hard to see, but when you play a card you put it at the front of the hexagonal base so that the arrows point away. You then leave the card and move your model to the other side of the card, pointing the way the arrow is pointing, while adjusting the speed and altitude with the dials on the base.

Note the dials and arrows.