0 used to show when it is necessary or would be a good thing to perform the activity referred to by the following verb: --
Mum ought to be home from work by now, so I'll give her a ring.
Your rash ought to clear up quickly if you use this ointment regularly.
This sauce needs a bit of flavour - I know, some lemon juice ought to do the trick.
In theory, the journey ought to take three hours, but in practice it usually takes four because of roadworks.
Men and women ought to be able to compete for jobs on an equal footing.
Whoever uprooted that tree ought to be ashamed of themselves.