Gray card? K mode?

[ilovemy50d]

I'm still really confused on how to get the right white balance. I bought a gray card (I haven't used it yet), I've discovered K mode, and just start shooting in RAW. Do I need to be using all of these 'tools' to get the right white balance?
And honestly, I don't even know what is the right white balance. Although, I can tell you when it's off.
Any suggestions, tips or tricks would be helpful! TIA!