SHOULD

We use "should" to give a piece of advice AND/OR when we think something is a right a thing to do.

Example: I think helping the homeless is a right thing to do, so I say "People should help the homless".

When you have a stomach ache, I will say "You should see a doctor".

HAVE TO

1.We use "have to" to talk about obligations 

- Children have to go to school.-

- Men over eighteen have to go to the army.-

2. when we have no choice 

- I have to go or I'll miss my train

- When I was a kid I had to eat soup before I could have some sweets.

3. when something is necessary

- You have to do sport to be fit

- you have to eat a lot of vegetables and fruit to be healthy

MUST

1. We use "must" to talk about stronger obligations.

-You must be silent in the library.

- You must turn off your mobile phone at the lesson.

- You must ot hand in your essay on time.

2. When you feel strong moral obligation INSIDE you

- This woman saved my life, I must help her.

- I must take care of my parents when they are old.

BUT

Negatives are a different story))

SHOULD NOT is the easiest part)

We use "shouldn't" to say about something that is wrong in our opinion

- You shouldn't talk stay out late, you will fell sleepy tomorrow! (just my opinion, IMHO))

Then comes DO NOT HAVE TO

We use "don't have to" to say that something is not necessary to do.

- We don't have to clean the table in this canteen. (the waiters usually do that).

- You din't have to go to the army in the USA. (but you can if you want, you have a choice).

- You don't have to be born in a rich family to be a millionair. (you can become rich later).

MUST NOT

We use "mustn't" to, again, talk about stonger obligations! )

- You mustn't smoke here!

- You mustn't wear jeans and a t-shirt to the office. (there is a dress code).

Should / have to/ must