If you created a second YouTube channel and you are want to link it to your original adsense account, then you are in the right place. It's not a hard thing to do. It's just that some of the peices are kind of hidden on YouTube's site.
I am going to assume that you have already created a second YouTube channel and that you want to link it to your adsense account. First, log into the YouTube channel that you want to tie to your adsense account.