If you zoom out enough, it'll end up looking a lot like the run of MHA/BNHA the anime series.
Many campaigns will omit the origin story bits and training arcs and just launch into the portion of the storyline where every PC is a fully functional superhero. YMMV. In any case, the usual champions campaign is going to start with stopping a bank heist and introduce them to existing hero organizations, law enforcement, villains and NPCs.
After some intervening run ins with recurring villains, PCs will eventually start picking up clues about something really big brewing. Often some aspect of their origin story or power source is going to have some resonance or even catalyst like effect on this BAD THING which sort of puts them squarely in the spotlight in trying to shut down this potentially existential crisis.
The big finale is the final push to putting a stopper in the big bads trying to bring their master plan to fruition. How much filler your insert between the start and end is up to you and your table.
If your PCs have a united element of their origins or background that can be leveraged to craft the ultimate plan of DOOM, so much the better. If you have an extremely random assortment of PCs, it will take much more creativity in involving everyone equally so it doesn't seem like any one PC is the focus of the campaign.