When you get off the plane, you'll be funneled down a long corridor. At the end you'll see yellow signs for ARRIVALS and purple signs for TRANSFERS. And you'll go down a small escalator. At the bottom, there'll be a bloke (or woman) basically shouting "arrivals/DC to the left, transfers to the right". Take the transfers route. You'll end up in the immigration hall, have your passport stamped (fingerprinted etc), collect bag(s) if appropriate and go through customs. Deposit bag (if appropriate) with UA personnel and head back up into main terminal (either C or D gates) for UA connection. If you are on a UAX (United Express) flight, you need to catch a mobile lounge to the commuter terminal (do a search for various horror stories there ).