some open item queries

hi,

i read about open item management and now have few queries.

1) account meant for open item manged only for clearing account?

2) i read this 'when you activate open item field in the Gl it means those accounts need to be cleared at the month end'.

my question is for clearing account then i quite agree but what about customer and vendor account in point 3? how to clear at month end?

3) i read the follows. what does it mean 'automatically set for customer and vendor account?

You can only clear open items that are posted to accounts that

are managed on an open item basis. Open item management is

automatically set for customer and vendor accounts. For G/l

accounts, however, you have to set the open item management

option in their master record yourself. Open item management

would usually be set for the following G/l accou

thanks