To forage is to wander around looking for food. When it’s cold and snowy outside, birds may forage for food in your backyard, digging around for whatever they can find.
The verb forage often describes animals searching for food, but it can also be applied to people. In those circumstances it retains the slightly desperate sense of coming up with whatever is available. For example, if you want to cook dinner but have no time to go to the grocery store, you might forage your refrigerator and cabinets to find good substitutes for ingredients in your recipe.