To highlight particular cells from the grids of an area in different colors or patterns in QGIS, you can follow these steps:
Open your QGIS project and load the grid layer that you want to highlight cells on.
Select the grid layer in the Layers panel and click on the "Layer Styling" button.
In the Layer Styling panel, select "Rule-based" rendering.
Click on the "+" button to add a new rule.
In the "Filter" field, enter the expression that will identify the cells you want to highlight. For example, if you want to highlight all cells where the "value" field is greater than 50, you could enter the expression "value > 50".
Click on the "Symbol" button to select the symbol you want to use for the highlighted cells. You can choose from a variety of colors and patterns.
Click "OK" to save your rule.
Repeat steps 4-7 for each additional rule you want to add. You can use different filters and symbols for each rule to highlight different subsets of cells.
Once you've created your rules, you should see the highlighted cells on the map. You can adjust the transparency, size, and other properties of the symbols in the Layer Styling panel to fine-tune the appearance of your highlights.