I cannot seem to figure out how to take and keep just the vocals out of a song. I mean to get rid of all the background music and to the background music myself for a cover.

I want to be able to do something like this.... (on the rap part)

I have Cubase 5 in case that helps. Thanks!
Oh hey, I didn't see you there
It's unbelievably complex and very nearly impossible to properly extract vocals from a mixed tune.

However, there's tons of 'vocal remover/karaoke' plugins and software that can do a rough juob by basically cutting out the stereo centre of the mix (which is where the vocals usually are). Results vary from dreadful to usable, depending on how the song was mixed, but it;s never going to sound amazing.

The simplest answer is to find a multitrack version of the song in question.

A few years ago this would've been impossible unless you happened to work for a major studio, but people have cleverly extracted mutlitracks from Guitar Hero and Rock Band, so if you're songs ever been featured in one of those games you're sorted. Search for 'rock band moggs' to get started.
There are also a few 'proper' multitracks out there; high quality and completely unmixed. I've got the original 32-track Bohemian Rhapsody and it's phenomenal.