SHOULD OR MUST

1) Should  
should  is used to give advice ,to make recommendations or to talk about what we think is right or wrong.
 positive form ; should
e.g. :
You should eat more slowly. 

 negative form  :shouldn't
e.g.
  You shouldn't work so much.












2) must
must is used to talk about an obligation or  probability .
positive form : must

e.g.
You must do your homework .

negative  form : mustn't

mustn't  is used  to forbid something ,it is forbidden, it is foolish to do it.
 e.g.

You mustn't be late .