I suggest reading very carefully and following the instructions EXACTLY. No offense, but you do sound really inexperienced with flashing and android. Then again you DID call yourself a noob. lol.
Anyways, You probably read backing up before flashing as in backing up your current android setup. Usually before flashing anything in android, its wise to backup your ROM in case anything goes wrong. You will get around to this another time. As far as backing up webOS, just backup your photos, videos, etc., stuff like that if you wish.
The SD Card doesnt refer to an actual memory card. It means your internal memory. So when it says, place zip on root of sd card, it just means put it in the internal memory. In android, its labled "SDcard"
If anything goes wrong, you always have the webOS doctor to restore everything. Good luck.