The game ends as soon as one side has no seeds left. The other player keeps the seeds on their own side, and the larger store wins.
After any move, if every pit on one side is empty, the game is over. The player who still has seeds on their side moves all of them into their own store, and then the stores are compared. The player with more seeds in their store wins.
Why hoarding works
Seeds left on your side at the end are yours, which is why emptying your own row early is rarely a good idea and why running your opponent out of seeds can be a strong plan. The stores can also finish level, which is a draw.
To plan the endgame, read the Mancala strategy guide, and for the sowing rules themselves how to play Mancala.