I'm a @PlayOverwatch noob (just made it out of bronze). When watching OW content, a lot of the analysts talk about creating space. I get the general idea, but I'm looking for some more beginner focused content that can explain the essential parts of it. Halp?
Adding to what Ace said, if team A lacks proper hitscan DPS, phara/mercy can force a team off highground. Flip side of this is team B can go widowmaker to clear the skies of said pharmacy thus creating space for team B to advance.