So recently i bought a carrera vengeance for £45 which is a bargain and the only problem was the gears(24 gear SRAM shifters) for the left side. When i got it i tried to shift but it just clicks and nothing happens, there is also a strong resistance. Someone please help.
If there is a strong resistance. My guess is that you have a limit screw preventing the fron derailleur shifting to bigger chainring.
Check limit screw
Check if front derailleur can move freely (unscrew both limit screw and pull the cable to see if front derailleur move). Sometimes front derailleur corrodes to the point that it cannot be moved.