Mount

A old photograph on a decorated mount

Mount has three main meanings.

Mountain

"Mount" is often used to mean "mountain", as part of a name e.g. Mount Vesuvius, Mount McKinley, Mount Everest.

To "mount" something means to put it onto something else.

An artist mounts his paintings on cardboard. An architect mounts his models on foamcore.
A camera is mounted on a tripod. A gun is mounted on the deck of a ship.
A rider mounts a horse. A gymnast mounts the balance beam for a display.

A "mount" is a thing for mounting something on.

It might be a piece of equipment such as:

A lens mount for a camera. This is the part of the camera that is made specially so that lenses can be attached.

It might be a piece of stiff flat "backing" such as:

A mount for a stuffed animal. This is a piece of polished wood that a stuffed animal can be fixed to, for display.
A picture mount. This is a piece of cardboard which a photograph or other picture is attached to.

It might be an animal:

"Frederick's mount was a fine black horse, Ernest's mount was a chestnut mare, Clumsy Jack's mount was a skinny old goat."

Mount (in computing), the process of making a file system accessible
Mount Unix, the utility in Unix-like operating systems which mounts file systems
Mount (streaming), a concept used in streaming software programs