So this metronome thing is really confusing me. When should a metronome be used? Let me expand on what I'm trying to ask. For example, I use a metronome to practice technical stuff such as scales, speeding up my strumming, and all that. But when it comes to applying the use of a metronome to a song, I'm very very lost on where to start. For example, sheet music has the notes and timing given so you can open a metronome and practice it, slow it down a tempo and practice, but lets say I see this song in youtube which happens to not have any sheet music. I've figured out the bpm/tempo of the song and searched for a chord sheet with the lyrics. There is no tablature for this song. How would a metronome be effective in learning this song? Currently Im just using the song as a timekeeper and reference and learning it that way. But I hear people say all the time to use a metronome to learn song and for classical or sheet music with notes and tabs with timing is understandable, but for the situation I described, please help.

I can understand the use of a metronome to learn the song if lets say I come across a section and I know the tempo of the song, I slow it down in the metronome and practice it.

Please, someone, clarify further.