Message1, Message2 and Message3 are variables that contains some data. (in this case Message1 was filled with "Hello", Message2 with "world" and Message3 with "!")
When you use the function "echo(Message1 .. " " .. Message2 .. Message3)" the double dot (..) is the symbol to say LUA you want to concatenate (add what's before this symbol with what is after it), the " " is the space character (hardcoded, meaning it will always be added and will always be a space character at this position in the whole expression).
That's how, in the end you get:
Hello_world! The underscore (_) representing the space character
Message1 .. " " .. Message2 .. Message3
That's paraphrasing the original tutorial but I hope it cleared things for you.
Last edited by Kyat; Jan 9, 2011 at 02:11 AM.