Foley versus ambience
Foley is a sound made by a specific action: a footstep, a door, paper, glass, water. Ambience is the sound of a place over time: rain, a forest, a city street, an empty room. Film and game sound uses both together; producers layer them under beats for texture and a sense of space.
What makes a good recording
For foley, look for close, dry recordings of a single action, so you can place them with your own reverb. For ambience, look for long continuous takes without voices, music or passing traffic, which make loops obvious and can hide rights you didn't expect. Stereo and binaural recordings give the strongest sense of place.
Where the free recordings come from
Field recordists share a great deal of their work under CC0 and CC BY on Freesound and Wikimedia Commons, and game audio packs add clean foley. The BBC Sound Effects archive holds decades of professional recordings under personal, educational and research terms, so its results carry a non-commercial verdict.