What does it mean when it says to drive trough a corner a car must stop a minimum number of times? I know it means the yellow number, does it mean slowing down the number of gears?
Your car must end it's turn that many times in that corner. e.g. If a turn requires 1 stop, you must end a turn within the confine of the corner (or face wear point/tire penalties.)
The gear you are in doesn't matter. if you get lucky you could be in 6th gear for a 1 stop turn. (or face a fiery death if you are unlucky).
On 2+ stop turns you must end that many turns in the corner.
When you slipstream if you decide to pass the car infront then cut back in front of it do you roll for collision passing next to it? and the same if you change lane and move 2 spaces forward past the other car does it cause a collision?
You only roll for a collision when your turn ends adjacent to another car. It doesn't matter how close you come while moving.