The word mount has several meanings:

1. To climb up onto something, especially a horse or bicycle. When you mount a horse, you pull yourself up into the saddle. Knights in medieval times would mount their horses before battle. You might also mount a stage to give a speech, or mount the stairs to reach the second floor.
2. To organize and carry out something significant, like an expedition or campaign. A school might mount a fundraising drive to buy new playground equipment. Explorers mount expeditions to distant places. Museums mount exhibitions of artwork or artifacts. This meaning involves careful planning and effort: you assemble all the pieces needed to make something happen, from gathering resources to coordinating people to setting everything in motion.
3. To attach or fix something in position. You might mount a picture on the wall or mount a telescope on a tripod so it stays steady. Scientists mount specimens on slides to study them under microscopes. A mounted police officer rides a horse while on patrol.

Something that you climb onto, like a horse, can also be called a mount.