When it comes to the relationship of the quantum number L and a subshell, we say that the shell of an atom can be further divided into subshells, also sometimes called sublevels, with each one assigned a variable letter. We're going to say the value for the angular momentum quantum number L can determine this subshell letter.
So here if we look we have values for L as 0, 1, 2, and 3. When L=0, the subshell letter is S. When L=1, then it's P. When L=2, it's D, and when L=3, it's F. So just remember if you know the L value, you know the subshell letter.
If you know the subshell letter, then you know what your L value will be. So just remember the order in terms of each of these subshell letters and the number associated with them.