local p = -- Defines a variable p as an empty table, but *not* nil.
function p.main(frame) -- This block defines the table element p["main"] as a function. return "I don't know. Wow!" -- The string result of the function.end -- Ends the block defining the function object p["main"] (or p.main).
return p -- This returns the table p, which under the key "main" contains the -- function above (p.main), which when called returns string "Hello world".