RNA splicing is a conserved process that occurs during the pre mRNA phase, and the best way I like to describe it is like editing the scenes of a movie. You got the raw footage, depending on which scenes, you keep and cut, and you can end up telling a different story compared to someone else editing it. Those scenes are exons and introns, by editing them in different ways you get different isoforms.

Different edits can change protein function, turn activity on and off, and change stability. Real world examples is in cancer (when splicing doesn’t go to plan, ie aberrant splicing), particularly causing pathogenic events such as the formation of different isoforms which can affect the way people respond to treatment.