Server browser.
Pick a server. Click connect. Deadlock opens and joins.
Connect
How connect works.
Click Connect on any live server. Your browser hands off a steam:// link to Steam. Steam launches Deadlock and joins the server directly.
If nothing happens, Deadlock might not be installed, or Steam is blocking the protocol. Open console in-game and type connect <ip>:<port> manually using the address shown on the row.