There's not just one simple answer, unfortunately. But here's a potted summary:
(1) Used for polite requests in the present - 'Could I have a cup of tea?' (2) Used to talk about ability in the past- 'When I was five I could ride a bike.' (3) Used to talk about possible situations in the present you are making a guess about - 'This photo could be in France, but I'm not sure.' (4) + have - Used to talk about possible situations in the past. 'The murderer could have left by the window.'
(1) Used to give advice about the present - 'You should go to bed - you look tired.' (2) + have - Used to criticise an action in the past - 'I shouldn't have said that.'
(1) Used for strong obligation, usually by an authority figure. (Unlike 'have to') - "You mustn't touch this button, or the machine will stop.'
(2) Used to make strong suggestions in spoken English - 'You must come and visit sometime.' (3) Used to talk about deductions or guesses you are fairly sure are true- 'The ground is wet, it must have rained.'
(1) Used to give advice or recommendations about the present- 'You ought to be careful.' (2) Used to criticise past actions 'I ought to have posted this letter yesterday, but I forgot.'