Perhaps you are at college studying COBOL which is why you are asking basic questions. We do not give answers but point you in the right direction (hopefully). One of the right directions is paying attention in class. Another is doing your reading - of a good book on COBOL and/or the COBOL manuals - in particular the language reference. Do not think you do not need the manuals - I have been referring to them today - and that is after 30+ years experience!
The problem I have is that people can explain things quickly but I can only comprehend slowly.