96 buick PA won't start nor crank it clicks and nothing I tried to turn the crank with a pipe and wouldn't turn . How do I fix this to drive it again?

I'd check the starter.

Well start with the battery then the starter.

I had a mechanic look at it he said it was the battery but I put a new one he said the motor was lock bc the crank wouldn't turn . But how could I unlock it or if I change the statter that would unlock it?

If the engine is locked up it's junk. Lucky for you because the 3.8 liter or 3800 is in a ton of GM cars like: Bonneville, lesabre, delta 88, 98 Oldsmobile, Riviera, Regal, Transport van, silhouette van and more. So if the car is worth it to you get one out of a junkyard. As far as turning it over with a pipe, you need to remove the belt and get on the crank pully bolt with a socket and try to turn the engine with a big breaker bar. If it moves then the engine is not locked up and junk. Then a starter might work.