how to redflag a value if it drops below a set number

Hi,
i am trying to make an inventory spreadsheet for work. I want excel to highlight the inventory when it gets below a certain number so that I will know it is time to reorder more. How do I do this?

Go to conditional formating.

There you can select "cell value is less than" and select the cell to go red.
Apply same format to all cells as needed