That's a nice tutorial, but if you want to use a normal command, for wich you don't need an adminlevel, you could use this:
/*
Hello world, v0.1
By JGHG
*/
#include <amxmod>
#include <amxmisc>
public myfunction(id,level,cid) {
client_print(0,print_center,"Hello world!!!")
return...