Go (game)
The playing pieces are called "stones". One player uses the white stones and the other, black. The players take turns placing the stones on the vacant intersections ("points") of a board. Once placed on the board, stones may not be moved, but stones are removed from the board if "captured". Capture happens when a stone or group of stones is surrounded by opposing stones on all orthogonally-adjacent points. The game proceeds until neither player wishes to make another move. When a game concludes, the winner is determined by counting each player's surrounded territory along with captured stones and komi (points added to the score of the player with the white stones as compensation for playing second). Games may also be terminated by resignation. A teacher might simplify the explanation by saying to a student "you may place your stone on any point on the board, but if I surround that stone, I will remove it."
Go (game)
The general strategy is to expand one's territory, attack the opponent's weak groups (groups that can be killed), and always stay mindful of the "life status" of one's own groups. The liberties of groups are countable. Situations where mutually opposing groups must capture each other or die are called capturing races, or "semeai". In a capturing race, the group with more liberties (and/or better "shape") will ultimately be able to capture the opponent's stones. Capturing races and the elements of life or death are the primary challenges of Go.