First we are given a value for the principal quantum number "n":
This value of "n" can have the following values for the orbital angular momentum quantum number "l":
These values of "l" can have the following values of the magnetic quantum number "ml":
The highlighted set is the one given in this question, This corresponds to a single atomic orbital in the "2p" subshell. A single atomic orbital can only hold two electrons because the spin quantum number "ms" for an electron only has allowed values of +1/2 and -1/2.