what does the magnetic quantum number determine?

the magnetic quantum number determines  the shell as well as the orientation of an electron in an atom,

what are the possible values of the magnetic quantum number ml?

for the magnetic quantum number ( m) it value depends on the value of  l , for example The magnetic quantum number (m) can be any integer between -l and +l. If l = 2, m can be either -2, -1, 0, +1, or +2.

what does the first quantum number (n) describe

   the 1^st quantum number ( n) describe the size of the orbital, it as value from, it takes value from 1 and the size increases as the number increases, orbitals with quantum number 1 is larger than orbital with quantum number 2.

what does the second quantum number (l) describe

The 2^nd quantum number describe the shape of the orbital, it takes value from 0 upwards,  where 0 is spherical, 1 is spherical, 2 is cloverleaf and even a more complex shape .