0 used to say or ask what is the correct or best thing to do: --
You should take the bus - it's the easiest way to get there.
You should be ashamed of yourselves.
There should be an investigation into the cause of the disaster.
I should have written to her but I haven't had time.
You shouldn't have said anything.
It's rather cold in here. Should I (= do you want me to) turn the heating on?
3 used after "why" when giving or asking the reason for something: --
4 used instead of "would" when the subject is "I" or "we": --
We can complete it step by step however long the road is and it can't be completed however short the road is if you don't even mark your footprint.
Vi kan slutföra det steg för steg hur lång vägen än är och den kan inte slutföras hur kort vägen än är om du inte ens markerar ditt fotavtryck.