We use 'should' for giving advice.

We use 'should' to give an opinion or a recommendation.

'should' expresses a personal opinion and is much weaker and more personal than 'must' or 'have to'. It is often introduced by ' I think'.

We can use 'should' after 'reporting verbs' such as
demand  insist  propose  recommend  suggest

However, it is also possible to say exactly the same thing by omitting the 'should' and just using the infinitive form without 'to' . Some people call this the 'subjunctive' form.

We can use 'should' after various adjectives. Typical examples are :
funny  interesting  natural  odd  strange  surprised  surprising  typical

We can use 'should' in 'if clauses' when we believe that the possibility of something happening is small.

We use 'should' in various fixed expressions.
To show strong agreement

To express pleasure when you receive a gift

To emphasize  a visible emotion