Tinning is coating the conductor of a wire in solder ready for soldering. This makes it very easy to solder, especially onto hard to solder places.

Start by stripping your wire, but before you pull the sleeving off, twist it while pulling it off. You must twist in the same direction the cores are twisted. This leaves a nice tightly twisted conductor. Then rest the exposed core on the iron and dab the solder onto it. Don't use too much solder.

When you come to soldering the wire onto a conductor, you can just heat it up and you're done!