The select command, will allow you to chose which memo folder will be your active memo box. The CLOSE command would close a selected memo folder. You have 3 default memo folders, INBOX, SYSTEM and RECYCLER You can create additional folders, see create.
Example:
/msg memoserv select SYSTEM
You need to select a folder before you can list or read the memos in it. You can select a new folder without closing the old one; it will close for you when a different folder becomes active.