Black plays first, so Black has a slight advantage. To even it out, a fixed number of points is added to White's territory after the game. That's "komi." In Japanese professional tournaments, it's basically 6.5 points.
POINT 01
Paying back Black's advantage of moving first, in points.
Go starts with Black. Being able to play the first move freely is a big advantage; without any adjustment, Black would win more easily. So after the game, 6.5 points of komi are added to White's territory to decide the winner.
For example, even if Black's territory is 6 points more than White's when counted, adding komi gives White a half-point win. Black needs a lead big enough to win even after komi.
POINT 02
Because of the "half point," there are no draws.
Komi includes a half point (0.5 point) to eliminate draws. Territory is counted in units of 1 point, so adding a half point means someone always wins. That's why results come with a half point, like "W+0.5" or "B+3.5."
- W+○.5: White, with komi added, came out ahead
- B+○.5: Black came out ahead even after komi
- Win by resignation: the opponent resigned midway (points aren't counted)
POINT 03
Catch the commentator's "komi is heavy."
When the commentator says in the middle game "Can Black give komi?" or "Komi is heavy," the question is whether Black's lead can exceed the 6.5 points of komi. Even if Black is slightly ahead, adding komi can put White ahead. In close games like that, the endgame decides the result.