A really simplified explanation: the wind pushes the kite, which unreels the kite string, which spins the generator shaft to generate electricity.

When the kite string runs out, the kite folds up or changes its orientation so the wind isn’t pushing it anymore, and the generator reels in the kite string.

When the kite string is reeled in far enough, the kite catches the wind again, the kite string starts unreeling again, repeat as long as there’s wind.

It’s actually, I think, a really creative implementation of wind power.