Guild check rooms are a place for new players to get the equipment
(armor and weapons) they need when they're first starting out.  They
can be found in each of the primary guildhalls.  Equipment in the
check room is provided by higher level members of the guild, who earn
dues by checking them in.  Lower level characters can then pay that
same amount of dues and receive those items for their own use.  Each
character donating items can only check in a single of each type of
item at a time and may not donate another until the first item of
that type has been checked out.  Items checked out are automatically
threaded to the person who checks them out and may not be exchanged
for guild credit at the threaded item shop.  Only characters of lower
level than the character who checked an item in may check them out
again.

Each guild has its own guidelines for what items can be checked in.
For more detail on your guild's own guidelines, as well as for syntax
on how to use the check room, consult the sign in the room itself.

Characters may also energize PE (HELP ENERGIZE) in the guild check
room.