They are usually open to the general public for a fee. Some museums have free entrance, either permanently or on special days, e.g. once per week or year.
The museum is usually run by a curator, who has a staff that cares for the objects and arranges their display. Many museums have associated research institutes, who are frequently involved with studies related to the museum's items.
Either the museum itself or an associated institute may organize expeditions to acquire more items for the museum, an activity famously depicted in the opening of the movie Raiders of the Lost Ark.
Museums may also acquire items through donations, sales or trades. For instance, a museum featuring Impressionist art may receive a donation of a Cubist work which simply cannot be fit into the museum's exhibits, but it can be used to help acquire a more relevant painting. Larger museums will have an "Acquisitions Department" whose staff is engaged fulltime in this kind of activity.
Museums often cooperate to sponsor joint and often traveling exhibits on particular subjects where one museum may not have a sufficient collection or where the greatest works on a subject are collected. This exhibits have limited engagements, and are often require an additional entry fee.