Press the ~ key (on some keyboards it's ` or ¬) (with or without pressing shift, it's immediately left of the 1 key, above Tab on most keyboards) and the game will pause, bringing down a black window that you can type into.

@LITTLE-CHILDREN (View Post)
1. It's Lua, not LUA, it's NOT an acronyme, it's moon in Portuguese
2. Try with the on screen keyboard
3. If that doesn't work, Simon or Cracker64 made a Lua Script to open the console when your cursor is at the upper left corner, I'm gonna get you the link in a sec..

@LITTLE-CHILDREN (View Post)
http://minus.com/mbUO1rK

Download that, save it a autorun.lua and put it into the Powder Toy folder.
Should work just fine :)

@LITTLE-CHILDREN (View Post)
Thank Cracker64 for creating the script ( Or Simon can't remember )