If it's just the filter it will fit strait in as the other filter you take out if they make one or are you on about an induction kit fitting instruction will be on the box
I have seen one fitted directly to the air intake without the air box fitted,
How does this affect the performance and running of the car?
You mite get 1 or 2 hp out of it depend's where it's fitted if you got cold air feed. If it's too close to the engine you will get heat soak warm air going into the intake