Newbie question regarding gifted iPod w/ music

My children gave me an iPod (80GB video iPod) and they populated it with music & video from various sources - ripped CDs, downloaded mp3 (converted for iPod), home video, etc.

When I connect my iPod to my computer (running iTunes), I am presented with a message box saying my iPod is synched with another iTunes library (my son's) and I am given two choices:

1) "Erase and Synch" - erase everything on my iPod and synch with my library

2) "Transfer Purchases" - copies iTunes store purchases this computer is autorized to play from this iPod to this iTunes library.

I am confused... I certainly don't want to erase my iPod - full of videos of my grandchildren and music I like and I know nothing about iTunes purchases or authorization. I have never been to the Apple music store or purchased any music from Apple although my son has.

Can anyone explain these options and offer advice? At this point, iTunes will not display my iPod content since I have not made a choice between the options identified above; I can only see the contents of my library.

Thanks in advance... geez, I thought the Apple/Mac/iPod experience was supposed to be so easy and cool.