How do you get a helocopter in GTAiv?

Answer 1

You can get them at the helitours in lower algonquin, or you can spawn an Annihilator (police helicopter) by dialing 359 555 0100 on your cellphone (cheat)

Answer 2

To get in the helicopter, you should simply have to press the "Enter Vehicle" button (varies from console to console, on the Xbox 360 it's the Y button).