the word 'should' is an auxiliary and is used as a part of speech in a few different scenarios. It is used to indicate something that one believes they have to do, or something the have already done. For example, if a person believes that they have to go to the store to buy milk, they can say 'I should go to the store.' It is also used to indicate something that one ought to do in the present or future; for example, 'I should think before I act.'
1.The customer should read the product instructions before assembling.
2.We should thank the teachers for their efforts in the classroom.
3.The team should have started the project by now.
informal usage of the word 'should' is often used as an equivalent to the word 'must'. In the past tense it is often written as 'should’ve' to denote something that didn’t happen but ought to have. It is important to note that the verb phrase 'be supposed to' also carries a similar meaning. In the imperative form, the word 'should' can be used to express a polite request or suggestion.