It works like it does for other cells. You didn't post any code so we cannot see what you've tried nor what you're trying to do but if you're data binding then you shouldn't need to read it directly anyway. DGV will bind the cell value to the boolean you're backing it with.
But if you need to read it then you'll go to the cell that has the checkbox and read the Value
property, which is an object. Cast it to a boolean (assuming only true/false values). Alternative you can cast the cell to the DataGridViewCheckBoxCell if you need something more.