MODFLOW is a groundwater flow model. It does not measure groundwater, but it does simulate groundwater flow by solving the differential equations that quantify the flow. You can model the impact of groundwater use on the groundwater reservoir. I recommend you read the text "Applied Groundwater Modeling: Simulation of Flow and Advective Transport" by Anderson and Woessner. You will find all of the input requirements in that text.
The above answer is correct. You would need material properties including hydraulic conductivity and storativity (or porosity), you will need spatial/temporal boundary conditions, and you will need hydraulic head measurements collected from groundwater wells.