EV = Expected Value
= Your expected return on a wager.
Taking a simple example...
You push preflop for 1000 chips total from the small blind, Villain has 100 chips also in the big blind and calls, and it turns out you are a 70/30 favourite. You work out your EV by multiplying the possible outcomes by the probability of that outcome and adding them together. So in this example...
EV = (0.7*2000) + (0.3*0) = 1400
Here, the 0.7*2000 reflects the 70% chance you will double up to 2000 chips, likewise the 0.3*0 reflects the 30% chance you will bust. As you can expect to finish the hand with 1400 chips on average
, the EV of your push given that villain called is +400 chips. Constrastingly, Villain's EV (assuming he has 100 chips like you) is (0.3*2000) + (0.7*0) = 600 = -400. On average he will have 400 less chips than he started the hand with (which makes sense, as your +400 EV has to come from somewhere ).
This obviously gets a lot more complicated once you start calculating for ranges of hands that villain can hold, probabilities of villain folding to bets, and so on and so forth, but that's the basic premise of EV. I can do a more complex example if you like, just let me know.
Fold equity is the extra value you get from making a bet if your opponent(s) fold. If you're shortstacked and have say 3 big blinds and push from the small blind into the big blind who happens to be chipleader, your fold equity is very small, as it is very unlikely he will fold. If you raise 4BBs preflop UTG on the bubble of a tournament, for example, your fold equity is considerably larger.