the answers have given the forms but not the reasons nor the rules
for contracctions - the apostrophe is a tombstone for a missing letter.
and so folk-sill - the front bit of a ship is spelt long forecastle but can be foc's'le - and you will notice there aren't enough apostophes for the missing letters
is not becomes ... isn't .....and does not becomes doesn't
the long for ( not able to ) has to be cannot [double n and joined] but the short is can't ( loses an n ]
and n't is not a word on its own as every word in English has to have a vowel. Pyx is the only exception - and "cwm bran" is not English
I am not is always I'm not and never I amn't
and the reverse - am I not is always aren't I - altho I are is never used.
oh, and you will be pleased to know that "could" has a silent l in it because Dr Johnson put one in in 1745. So that it looked like should and would. It doesnt need to - as it comes from the Dutch coud which never had an l
we all use dictionaries