Ev is calculated by taking what you expect to win, multiplied by the probability of winning, then subtracting what you expect to lose multiplied by the probability you actually will lose. For determining if a call is +Ev, it is as simple as this.

(P+B)*%win - B*%lose where P is the pot and B is your bet.

A value bet is +EV on the other hand takes into account the probability of villain calling with worse and how often he would have bet with worse should we have just called.

(P+B)*%win*%calls - B*%lose*%folds -Bx *%bets
where bx is the amount villain might bet on a later street should we have just called. Im really fuzzy about the above though...

A bluff is +EV by considering three things. The first is how much we expect to win multiplied by the probability of the bluff working. We then add the amount we expect to win multiplied by the probability of winning should we get called. Lastly, we subtract the amount we expect to lose multiplied by how often villain calls multiplied by how often villain wins should he call. I.E....

We have a flush draw on the flop and semibluff.
(P+B)*%Folds + (P+B)(36%) -(B)*%calls*54%= ev

so the three things are the %win, %lose, and %folds?