Firstly, you have to notice that there are more than 2 element symbols here. As a result, there must be a polyatomic ion involved.
Hopefully, you recognize NH4 as the polyatomic ion ammonium (which carries with it a +1 charge).
The anion here is Cl (which has a -1 charge, thereby balancing out the cation – nice!).
To name it, start with the cation. Here, it’s ammonium. For the anion, when an atom becomes negatively charged, we indicate that by changing its suffix to -ide. So, instead of chlorine, we’ll make it chloride.
So, this is ammonium chloride.