First understand that in western music every "key" contains some notes but not ALL notes. ALL of the notes are called "chromatic scale." Each "key" contains a different SUBSET of those notes in the "chromatic" scale.

So...if you were merely to "give it the key of the song" as you suggest -- it will, in theory, "correct" every note to one of the notes within that key. However, in many cases that is NOT what you want -- since many melodies include notes that are NOT in the song's KEY. And many songs modulate (change keys)midstream. So if you "give it the key of the song" -- Autotune COULD be "correcting" some notes to the WRONG note.

There are 3 ways solve this to accomodate those "non-key" notes.

1) Change the key of Auto-Tune in real time while the song is playing back(or being recorded).

2) Bouncing a vocal track (i.e. "printing the effect") and stopping and starting the 2480 playback to change the key in Autotune...or

3) (AND THIS SOUNDS LIKE WHAT YOU ARE LOOKING FOR!) Set Autotune to "chromatic" (and also to "Major scale"). Those 2 settings ("chromatic" "Major") will give you the "fully automatic" functioning you seek -- and removes any requirement of knowing anything about keys or music theory or having to change anything midsong. This is because "chromatic" includes EVERY note of western style music. And Autotune will simply correct to the closest one of those notes. Voila!

You then should adjust the two side-by-side controls that control "speed" (how fast it corrects a note when it hears it) and degree of "choosiness" (I forget what the official name for this is -- but it controls how sensitive Auto-tune is) in order get as "much" or as "little" of the correction effect as you want without getting noticeable artifacts.

Of course to GET THE OPTIMAL PERFORMANCE out of Autotune, you may want these settings to change throughout the course of the performance -- which is why some people bounce different sections of their vocal using different Autotune settings. Again, you can stop the playback during a bounce -- make an adjustment -- and go on.

Lastly, you just have to set what kind of voice you're using it on (low male voice, tenor, soprano, etc) and that's it.

So, really, it CAN be pretty automatic and simple if you set it to "chromatic" and find the optimal settings for the other two controls.

It'll work that way -- and be COMPLETELY AUTOMATIC and help -- but it WON'T be the OPTIMAL result possible from AutoTune.

If the above does not clarify it for you, I'm not clear what is confusing you.