Hello,
I do know that "Shall" is used for future and "Should" is the past form of that. However, looking up in my dictionary, I have been confused about the real differnce between "shall" and "should". Because they are used in the same way in given examples.
Would you please help me?
'Should' is etmologically the past tense of 'shall' but in practice does not function as an independent past tense: that is to say, a main clause predicated by 'should' has either present or future reference, but not past.
The formal connection between 'shall' and 'should' is evident only in the context of reported speech, so that e.g. the statement
"I shall be here at seven tomorrow."
could (in BrE, at least) be reported as
I told her that I should be there at seven the following day.
(AmE speakers, however - and indeed many contemporary BrE speakers -would prefer 'would' here.)
Within a main clause , 'should' functions both as a DEONTIC modal, with the meaning '(have) a duty to/(be) obliged to', as in
You should always handle antiques with care.
and as an EPISTEMIC modal, with the meaning 'can logically be expected to', as in
His train has just arrived; so he should be here somewhere.
I hope this contains at least some of the information that you require!