Pure freighters have a completely open interior. There is usually space behind the cockpit for the crew to move about. Many freighters have moving load floors to assist with freight placement. Usually, freighters are equipped with lavs. About galleys, I am uncertain. For longer flights, there probably is some provision for crew meals and rest.
There are airliners in service which are combi layout - meaning they carry both passengers and freight. Usually, the passengers sit in the forward half or two-thirds of the plane, and the freight occupies the rear section. Passengers board the aircraft the normal way - through forward doors. Freight is loaded through an upward-hinged cargo door at the back of the aircraft, usually on the left hand side. Combi aircraft have full provisions for carriage of passengers - galleys, lavs,passenger service units, etc., up front so they differ very little from all-passenger aircraft.
UPS has become known lately for operating convertible freighters. It uses its 727-100QCs in this way. The seats (on special pallets) and airliner interior (overhead bins, galley, etc.) are loaded on when the aircraft is empty, and installed by a special crew. When the passenger flight has been completed, the aircraft is converted back to the freighter configuration.