"I tried to sear scallops and all this liquid came out into the pan–and I couldn't get them to brown. What did I do wrong?"
It's not you, it's the scallops. It sounds like the scallops you bought were "wet"–meaning they were soaked in a phosphate solution that makes them look whiter and plumper. But they are plump because they are retaining water, and as soon as they get near the heat, the water and phosphate begin to drain, and you'll see white, slightly foamy liquid in the pan.
Look for scallops marked "Dry" or Dry-packed". Fresh or frozen, these may seem more expensive but are actually a better deal–because you are not paying for water and soapy phosphate.