Fill the board with more discs of your color than your opponent has when the game ends.
Black moves first. On your turn, place one disc on an empty square where it traps one or more enemy discs in a straight line between your new disc and another disc you already own. Lines can go sideways, up and down, or diagonally. Every trapped disc flips to your color. If you have no legal move, your turn is passed automatically. If nobody can move, or the board is full, the game is over.
Count the discs at the end. The player with the most discs wins. Equal counts make a draw.
Corners are powerful because they cannot be flipped, so try to win them. Edges are usually safer than middle squares. Be careful with squares right next to an empty corner; they can give your opponent an easy corner. Look one move ahead and keep lots of legal moves open.