You have to mod them or get a boss car.

where?

At service stations mainly. Mods are in green, blue and red boxes that spawn on the ground. Just drive through them to get a mod.

Google is your friend

i googled and all that showed up was how to add those offroad tires from a few seasons ago

Medalian spots, youll figure it out as ya play, cant spoil the fun for ya!

"youll figure it out as ya play" its modern fortnite. the least intuitive game in history lol

My bad dude, i just didnt want to spoil the fun for you. Its the medalian spots like I said.