Here's how to break down the formula:

* (NH₄) represents the ammonium ion (NH₄⁺).

* [ZnCl₄] represents the tetrachlorozincate(II) anion.

* Zn represents zinc, with a +2 charge (indicated by the Roman numeral II).

* Cl₄ represents four chloride ions (Cl⁻).

The formula reflects the fact that two ammonium ions are needed to balance the -2 charge of the tetrachlorozincate(II) ion.