I want to change my pickups in my guitar Samick Trn-1 from humb neck on single coil.

How to plug that? I have problem with cables.

Can someone tell me how to install single coil to my gutiar?

But please, explain me this simple.

You need a pickup that will fill that spot. Look at Gibson p-94. That is the only one I know of off the top of my head.
Perhaps you could find someone trade trade you a guitar with a single coil already in it?