pls help ad-mod

[nownow]

i just installed ad-mod 1-1x2_v2-3 to my smf forum , on this theme http://www.smfthemes.org/index.php?theme=245

pls what is the next step, how do i add google add there, the system ask me to Please remember to always make regular backups of your sources and database before installing mods, especially beta versions. i dont really understand pls can somebody help and explain  it to me