How to use Print
The print function will take a string, number, or userdata as an argument. It casts the object to a string (meaning for userdata, tostring() is called on it and the __tostring metamethod of a metatable also applys). It will then send that string argument to the output window. Here is an example:
print("Hello world")
You usually see this in the new scripts that are freshly inserted in the workspace. This code will print "Hello world" (without quotes) in the output window.