There are three kinds of clefs: Treble, Tenor, and Bass Clef.
The Bass Clef is the lowest type of clef. This tells you that the second line from the top is F. So we have F to G to A and on.
Unlike Treble Clef which tells you that the second line from the bottom is G.
You would have to read more on it to completely understand but I do recommend this site :)
https://rockhill.instructure.com/courses/328/pages/treble-clef-and-bass-clef
