A unicycle is a bicycle with only one wheel. The "uni" at the start of the word means one, just like the "bi" on bicycle means two, and the "tri" on tricycle means three.
Because unicycles only have one wheel they are hard to ride and hard to steer, and they are not seen very often outside of circuses.
Something is uniform if it is the same everywhere. A wall that is all one color might be described as being a uniform shade of green.
A uniform is also the name given to the clothing all people in an organisation have to wear so they all look similar. People in the military wear uniforms, and many schools require that children wear uniforms.
Uniforms for men and women are often quite different, even in the same organisation.
A university is a place where people go, usually after finishing school, to learn more about something so they can get a job. Universities give you a degree or some other certification when you have finished learning. In some countries, a place where you go for other kinds of tertiary education is known by other names, like a college or a techical school.