Change a symbol of a single element in QGIS

If you want to change the symbol of a particular element in QGIS, you need to categorise the elements of its particular layer.

For example, let's assume that you want to create two different symbols with different colours, depending on the status of the caskets:

1. Green: inventoried
2. Purple: non-inventoried

You need to right-click on the layer. Then, custom the symbols and the properties depending on the values of a field.