If you have individual tracks without any existing metadata (other than possibly the file name) rather than releases with some metadata (either in tags or in the folder path), then you probably need to Scan the files to generate an acoustID and then use that to find the track. (Note: I only have albums, so I use clustering and lookup and so have zero experience of this myself.)
You probably also want to tweak the settings in Options/Metadata/Preferred Releases and possibly also Options/Advanced/Matching to match your particular needs.