insurance and "even money"

In Blackjack, I already have an idea about what insurance is. It is when the dealer has an Ace as his/her up card and he/she offers the players insurance. If the players take insurance and loss they only have to give up half their bet. Now what if the a player ties with the dealer or they both have a 21. I have hear that this has to do with a topic called "even money". Could you please explain that topic to me and explain a little on insurance. Thank you.