This video is an excerpt from my course, How to Read Sheet Music.
Let's take a look at the F clef. Here is the symbol:
Whichever line this clef is placed on is the F below middle C. For piano music it's placed on the fourth line from the bottom:
Notice how the two dots in the F clef symbol straddle this line? When placed on this fourth line up, it's called the bass clef.
The bass clef is therefore a type of F clef. (Nowadays, the F clef is only placed on the fourth line of the five-line staff, so the terms are sometimes used interchangeably. It's important to understand the difference in any case, and I advise using the terms precisely for clarity.)
Let's take a look at the F below middle C. Here it is notated on the staff:
Originally, the bass clef was created for the bass voice—the deepest of male vocal ranges. It is used in piano music to indicate low pitches.
Here are the notes on the lines and spaces of the bass clef:
For reference, I've included one ledger line below and above the staff. The first ledger line above the bass clef staff is middle C.
Many students are taught mnemonic devices to learn to read music. To learn the lines of the bass clef, the awkward mnemonic "Good Boys Do Fine Always" is typically used, with the first letter of each word indicating the notes on that line (bottom to top: G, B, D, F, A). For the spaces, the mnemonic "All Cows Eat Grass" is used.
Such devices may be useful memory aids, and if they are helpful to you in the very beginning stages, then I cannot object to your using them. I do not teach them, however, since I find them ineffective.
The professional method is to train the eyes to recognize reference notes and patterns. This is the method used in my highly successful course, How to Read Sheet Music. Upon completing the course you will be able to recognize notes on the treble clef and bass clef instantaneously!