Why does my car start one day and the next day it wont start? The car will crank but wont turn over

My car shifts gears & locks up on me sometimes. It has its days when it will start & wont start. One day it will crank and turn over then other days it wont turn over
My car has a manual transmission.

– Why does my car start one day and the next day it wont start? The car will crank but wont turn over