Extracting value from opponents is when you have a good idea, that your hand is the best hand, and you get the most value/chips back when you stack your opponent. You're trying to string them along when they have weak hands, and your hand is stronger without them making a better hand. It's good to practice making value bets, and it varies from player to player, not all players will call the same bets, or fold to them. Sometimes you need to change bet sizes to get value, or increase the likeliness of a fold.
I love trying to get the most out of every pot/hand, and extract value when I bet, the most your opponent is willing to call, or bet less to increase chances of a re raise. It's important to make sizeable bets, but also bet the most...