First you evaluate the distance between you and the subject. The focal length of your lens and camera sensor allow you to calculate at this distance the zone before and the zone after this distance that will be reasonably sharp.
For instance, with a Fuji X100F (lens is a 23mm) at f5.6 if you focus at 3m, the zone focus will be between 1,20m and 5,20m.
DOFmaster is a calculator that will help you find those charts for your lenses.
On my smartphone, I use DOF Calculator.