The Flash is a very fast superhero and can run more than a million miles in so many seconds. He is one of the greatest saviors of the DC Universe, helping to save a lot of civilians with just one fast reaction.
Some of the citizens don't even know who's helping them half the time and neither do the city's cops. He just hears about something from his friends at StarLabs and then is instantly off to the accident to sort it out. Even if just a simple accident is occurring in the city and he doesn't have his superhero suit on he helps out so fast that no one even knows what happened and everybody gets frozen for the time that he helps out the civilian.
Supergirl is the most powerful teenager on the planet.
Supergirl possesses all of of Superman's powers. She has his strength, speed and invulnerability all the way down to his flight enhanced senses. That's just a few facts about what Supergirl will be like before she comes onto television with the rest of the DC universe.
So I suppose you're now wondering what these two have in common.
A Gleeful Past
Both of these actors who play 'The Flash' and 'Supergirl' used to be in another show together. Grant Gustin (The Flash) used to be a singer of the Warblers in Glee while Melissa Benoist (Supergirl) used to be in Glee club on Glee. They didn't act much together on the show but knew each other from the show. Grant's character Sebastian used to be a real good singer and sometimes helped out the glee club with certain numbers. When he wasn't helping them he decided he'd bully some of them and throw slushies in their faces. While Melissa Benoist's character Marley was a very down to earth character who had a lot of trouble being in between two boys who both liked her. She always sang songs that benefited the glee club and her own life in certain ways.
These two actors wouldn't have acted together in many scenes because Melissa only came into the show in Season 4, while Grant was acting in it from Season 2 for only seven episodes because he wasn't a main character, whereas Melissa was one of the main characters. She was just brought in too late. She still knew some of the past actors though.
So now these two may work together in some crossover episodes if ever made of Flash and Supergirl. They'll soon get to know each other more now since both are heroes of the DC Universe.
"It's not being a hero. It's just doing the right thing."