How do I find out who my opponent is?

After the cup starts, check your Open Matches.

How do I contact my opponent?

Use match chat (click matches in the userbar at the bottom of your screen), add them in-game or in the chat below.

How do I find my opponent's Battle.net ID?

You can find it on the match page for your match, shown underneath their nickname and profile picture.

Where do I find the match page?

Click matches in the userbar at the bottom of your screen then click the joystick icon for your match.

Where is the bracket?

Click "Tournament Tree" in the sub menu above

Where do I upload replays

On the match page for each match you will find a link to "Upload replays".