Can : kunnen (vaardigheid & om toestemming vragen):
Can I talk to you in private?, I can lift this desk by myself!
Could: zou kunnen (vraag het beleefd & verleden tijd van can)
could I talk to you in private? , I could lift this desk by myself
should: zou moets (gebruikt om advies te geven)
I think you should brush your teeth twice a day
See pictures on p. 112