Can u put trigger shift gears or a bile with twist grip gears by jus swapping the shifter or would I not work

yes you can, messy but ok

Is it easy like n is it only 1 cable tar

Always best to fit new cable(s) when you do.Watch out for using Sram shifters with Shimano gears as some of their shifters pull a different amount of cable.
Try the CTC web site,tech section for all the info you need.A good sorce site for all cycling is the late Sheldon Brown's.It's the "bike bible".
Good luck.
Pete.

What rear mech are you using?

Remember to buy the correct speed shifter aswell.

Well I have a shit bike with good gears n getin another 1 with twist ones just want 2 swap them like could any1 do it for the right price thanks