how to fix sticky server drawers?

Pull the drawer out and check the wooden runners underneath. They often get dry and grind against the carcase rails. Rub a plain wax candle along both friction surfaces. This simple lubrication usually gets them gliding smoothly again.

what is a cellarette drawer for?

The deep drawer on a server often held wine bottles. Most have timber partitions to stop glass clinking together when the drawer moves. Some early ones retain a lead lining. This allowed the butler to pack ice around the wine before serving.

I bought an old dining room server last week and the gallery at the back is a bit loose on one side, is there a simple way to tighten it up?

Gently check how the gallery attaches to the main top. Many slot into small holes using wooden dowels, while others are held by brass brackets at the rear. If it uses wooden dowels, old animal glue tends to dry out and fracture over time. You might need to clean the socket out before reapplying a fresh adhesive. Never force the timber to move. Thin mahogany upstands snap easily if you bend them backwards.

My server has these little metal wheels on the bottom of the legs but they don't spin at all when I try to push it, should I oil them?

Those original brass castors seize up when dust and floor wax pack tightly into the housing. A drop of light machine oil can sometimes free the central pin. Usually it is safer to lift the piece rather than dragging it. Forcing a loaded carcase across a room on stuck wheels puts heavy strain on the leg joints.