Collaborative Filtering
This method predicts a user's interests by collecting preferences from many users. It assumes that if User A and User B agreed on something in the past, they are likely to agree again in the future. This is how Spotify suggests songs based on what similar listeners enjoy.
Content-Based Filtering
This method recommends items similar to those a user liked in the past, based on item attributes. If you watch many sci-fi movies, the system will recommend other sci-fi movies because of the genre tags, regardless of what other users think.