you just go to the link in the sheet (http://tinyurl.com/addSongSuggestion - we have just developed this form) and fill in your nick, artist, song title and paste ignition page link.
for difficulty rating, just enter what you feel it should be.
the info is then saved in google sheets table for review.
you are Int lead, Int rhythm and Adv bass.
I.e. for lead, if you feel the song is too easy for you, you rate it in lower class (beginner), if quite comfy and you feel you could do better after few tries,, rate it in your class (Int), if you see that the song is out of your reach, rate it higher class (Adv or MC).
If you really cannot tell, just select "I don't know"
the song will be tested by week creator anyway to check if rating is more or less correct.
Hope this helps.