Saturday (Oooh Oooh!) Word of Mouf Ludacris

how you gonna act like I don't push 'lacs

to "push" means to drive, possibly from the fact that when you drive a car you are making it travel forward as if pushed. so, he is wondering why you doubt he drives expensive cadillacs (maybe because you're jealous).
The artist is telling us that his Cadillac is broken, and must be pushed. He has probably run out of gas, or is having mechanical problems.