NH4Cl is an ionic compound, made from a positively-charged ammonium (NH4+) ion, and a negatively-charges chloride (Cl-) ion.
The NH4+ ion is, itself, held together with covalent bonds. that's what makes this Lewis Structure so interesting.
NH4+ contains one nitrogen atom and four hydrogen atoms. Normally this would make 9 valence electrons total, but the positive charge represents the loss of one electron (presumably to the chlorine in this example). This means it has just 8 electrons, enough to complete the octet on nitrogen with a single bond to each of the four hydrogen atoms.
You have to draw the NH4+ Lewis Dot Diagram in square brackets (with charge in upper right-hand corner) to show that it is an ion.
Similarly, chlorine, which normally brings seven valence electrons with it, now has a full eight. This completes its octet, makes it stable, and gives it a -1 charge. This is also drawn in square brackets.
Below, find a video of me drawing this structure step-by-step: