Open Portal using the edited shortcut.
Step 1: Console
Note the now-open console.
Step 2: What to Enter
Open or load a game, then pause (defaults to ESC or Pause/Break). Type "sv_cheats 1", hit enter, then do the same for "impulse 101" in the console (without quotes).
Step 3: How to Use
Unpause. Use the number keys to select weapons, and press the assigned "left portal fire" key to switch. The Portal Gun is available under "1". On-screen notes will tell you how to use each weapon
Step 4: Enter the Fray
Fight some turrets with the Crowbar and Gravity Gun!