A document is on the server and anyone with security rights can view it. Perhaps you now want to edit the document – it could be a word document. If you right-click and select Check Out (on the document in the hit list) the document will effectively be moved to your local PC and you can edit it.
Other FileDirector users will see you have checked it out and this means, crucially, that they cant edit it. Only you can.
So once you have made your changes, check it back in.