How do ants know exactly where to go in order to get that tasty little morsel?

Do ants just wander about until they stumble upon something delicious? And if so, how do they not get lost on the way back to the morsel when they go get other ants? Or do they hunt in packs and then send half the pack back to home base? How do they know to go around the tree, take a left at the jacuzzi, across the driveway and find the one cookie that fell off someones plate at my BBQ last week?