To mount is to climb up something, like a ladder, or get on the back of something, like a horse. You can also mount something on another object, like a camera on a tripod or a sticker on a notebook.
The word mountain can help you remember that one way to mount is to climb. You can mount a mountain or a flight of stairs. You can also mount a pony by getting on its back or a bicycle by climbing onto it. The oldest meaning of mount is, in fact, "mountain," from the Old French word mont, which has its root in the Latin montem for “mountain."