You gain them from winning.
They are for your character driver and your Bobs. You can select your own drivers (Bobs) from the little helmet logo on the GT menu screen and asign a suit and helmet to each.
To dress yourself in a suit go to the corner box at the very top left of the home screen and click, it will bring up your stats and the option to change suits.
The main purpose of them is to keep us happy while more updates are waited for. Also they can be used to create a team of Bobs all dressed in one particular colour/theme like a real race team.
