duga - to fit, to be useful/suitable/good for

duga duger dög dugt

Svampen duger inte att äta.
The mushroom is not suitable for eating.

Han duger inte till sjöman.
He is not good enough to be a sailor.

Den här duger ingenting till.
This is good for nothing.

Om den dög åt din syster, så duger den åt dig.
If it was good enough for your sister, then it'll be good enough for you.