Synching music on iPad Mini 2 question

I need help, iPad experts! I have an iPhone, but this is my first iPad. I put a bunch of music on it last month when I first got it, and now I want to update my playlists by adding a few things. But I get this whacky message saying it's going to ERASE everything including my movies, books and photos, and then replace it with every single song in my iTunes from my computer? I don't want that. But I'm not seeing any other option. I checked 'synch manually' but that doesn't seem to work the same as it does on my iPhone.

Please explain this madness to me... and then, if you know a work-around, please share it. (I don't use the iCloud by the way... I'm nervous about that, but maybe I should.)

Thanks!