Why a separate profile
The reasons are usually the same. Some need a smurf for the low bracket to play with friends without dragging them up in rating. Others learn a new position and would rather not damage the stats of their main. For the rest it is a spare way into the game if something happens to the primary one.
How it works
After payment you get a key. It issues a profile with the medal you picked. The rank is open, you can play right away — nothing extra to calibrate. The key arrives right after payment and gives you access to the account. A warranty replacement is handled in the same place.
Private software for Dota 2 is in the pricing section. The account and the software subscription are bought separately.