Theory:

Ought is an auxiliary verb; it takes the following verb "to" as its complement. This verb may appear either as a full infinitive (such as “to go”) or a bare infinitive (such as simple “go”), depending on region and speaker; the same range of meanings is possible in either case.
 
Ought to is a semi-modal verb because it is in some ways like a modal verb and some ways like a main verb. For example, unlike modal verbs, it is followed by to, but like modal verbs, it does not change form for person:
Example:
1. She ought to phone her parents.
2. You ought to have offered to help immediately after the accident.
3. He ought to respect senior citizens.
Ought to and should are similar in meaning. Should is more common than "ought to". Ought to is more formal than should.
Affirmative-
Ought to comes first in the verb phrase (after the subject and before another verb).Ought to cannot be used with another modal verb.
Example:
He ought to do more exercise.
Negative-
The negative is formed by adding ‘not’ after ought (ought not to).The negative of ought to is not common. We usually use shouldn’t or should not instead. We don’t use don’t, doesn’t, didn’t with ought to.
Example:
You oughtn’t to have said that about his father.
She ought not drink soo much during office hours.
The child ought not have told lies.
Questions-
The subject and ought to change position to form questions. We don’t use do, does, did.
Example:
Ought I to call the ambulance?
 
Important!
The question form of ought to is not very common. It is very formal. We usually use should instead.
 
Ought to: uses
 
We use ought to when talking about things which are desired or ideal.
 
Example:
Children ought to eat lots of fruit and vegetables every day.
 
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What is likely:
 
Example:
There ought to be more street lights near the beach.
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Reference:
dictionary.cambridge.org/grammar/british-grammar/ought-to