Complex sentence: Once placed on the board, stones may not be moved, but stones may be removed from the board if captured--this is done by surrounding an opposing stone or group of stones by occupying all orthogonally-adjacent points.
Split into simpler sentences: Once placed on the board, stones may not be moved, but stones may be removed from the board if captured. This is done by surrounding an opposing stone or group of stones by occupying all orthogonally-adjacent points.