A rectangular group of cells is called a Range. A Range must be rectangular, you can't have odd shapes; the smallest possible range is just one cell.

A ‘Range’ is defined by the top left and bottom right corner cells:

Notice the way the function is used to 'SUM' the range and the method of addressing the range: ‘C3:D7’.   Load the spreadsheet and write a formula to find the minimum value in the range