I need help with some of the functions on my Wii?

I would like some advice on on-line play for the Wii. Is there on-line play with friends that are on-line with a Wii? What is the Mii mingle feature for and why can't I select it? How do I locate a friends Wii if he is on-line? Sorry, it really started out as one question in my head, I swear. Promise, ten pts for best answer.