A Little Help About Adsense, anyone?

Just this morning, as I was browsing through my usual website routine I came across an Adsense topic and I got interested so I signed up for an account. Unfortunately, I used another e-mail address and another one here in Blogger, when I tried logging in here I got the address that I signed up for in my Adsense account and I tried changing it to this e-mail address but I can't cos another user is supposedly existing so I though it must be. I logged out and logged in using this one but it says the e-mail address doesn't exist in their records. Whatever. I'm so confused.

How does this thing work anyway?