Brake pad not tightening

[KS38]

       

Hi! We are new to bike ownership and have stumbled across a problem. Having bought a second hand bike for my son, the right hand rear brake pad isn’t moving when the brake is applied.
Also, the end of the cable in the lever on the left handlebar is twisted and not sitting correctly.
I’m hoping these are things we can rectify and would really appreciate advice on how. Thanks!

[Painkiller]

the cable n the top pic is seated correctly, check out the videos on this site or parktool site to set your brakes proper. and it is also time for some new rubber

[G_M]

Adding to painkiller's post: https://www.bikeride.com/adjust-v-brakes/