Form in music is the structure that holds up a piece. The big idea is that stuff repeats. Some forms have more repeated material that others. Rondo form is one of those.
Rondo form comes in several different flavors. Five-part rondo, as the name suggests, has five major sections outlined as ABACA. In prose: Something, then something else, then a return of the opening material, then something different followed by a return of the closing material.
Seven-part rondo has seven big sections outlined as ABACADA. Seven-part rondo can also look like this: ABACAB’A. This second type is called Sonata-Rondo as it actually behaves like a sonata-allegro form.
Rondos are not always clear cut. Each section does not have to end closed, though composers may do that. Some composers actively try to obscure form. The third and final movement of Beethoven’s Pathetique Sonata is a sonata-rondo form. However it’s not easy to hear.
Sections are often set apart by a change in melodic material; a change in key often comes with. In Sonata-Rondo form when B returns at B’ it’s often in a different key.
Like any other form the advantages of knowing where the large sections are divided is that a performer can make use of various levels of rubato. In addition to that, knowing form can help out when trying to connect ideas or really get into how a given section of music functions.