Equity is the amount in the pot that belongs to you. So if you have 70% chance to win the pot then you have 70% equity.
To calculate your pot equity, you need to multiply the size of the pot by the probability that you will win the hand (based on how many “outs” you have to win the hand.)
Suppose the pot was $100 and your equity is 60%. If you’re all-in and there are no other bets to call, then in the long run you’re expected to win .60 x 100 = $60.