A muck can contain a large number of items, so, how do you know what's yours and what isn't?
Well, as you wander round if you see a #number in brackets after its name this is either because you own it, or because it has an L, J or A flag (Link_OK, Jump_OK, Abode - worry about those later to see more read 'help flags' on the muck).
However, what if the items not in the room with you, how much can you do?
Well, do an '@owned' will list all items you own. You can always reference your objects by the dbref, that's the #number in brackets. This way, you can have multiple objects with the same name, and not get them messed up.
A very similar command is @find, but the @find and @owned commands have good help on the muck to help you restrict your search or display interesting information.