You'll be fine, i know it's overwhelming especially to get handed a rooted phone without knowing anything about it. I would recommend you install vortex, its close to stock but much better. Heres a link to vortex rc1
[ROM] VorteX RC1
you can download the rom zip right to you phone or download with your pc and transfer the zip to your sdcard. If you download it to right on your phone which i always do it's best to do it on wifi. Once you download it to your phone it will end up in your download folder. There should be a video on youtube on how to install vortex so just do a search of vortex rc1. The video is by DroidModd3rx, he's installing an older version of vortex if i remember right but the version your going to install gets installed the same way. We install roms in clockwork recovery which normally we use droid2 bootstrap to get in recovery but DO NOT use it since your on gummy or you will get in trouble. To get in clockwork recovery on gummy just long press your power button then you'll get a menu then press reboot and next press recovery then press the ok tab and your phone will reboot in recovery. Watch that youtube video and follow all the directions except the one where he says to use droid2 bootstrap to get in recovery. (again do not use droid2 bootstrap use your power button to get in recovery) if you have anymore questions just ask someone will help you.