A Little Help With M.A.M.E. on PS Vita RetroArch...(?)

[The_Dizzy_Vizzy]

So I've got MAME on RetroArch, but for the life of me I can't get the ROMS for it to work. I've been through numerous YouTube vids and search results on Google, but nothing seems to address this issue. I've tried all 3 available MAME cores to no avail. Any help would be greatly appreciated.

One more MAME question - how do I back out of a ROM on RetroArch without backing out of the entire RetroArch app?

Thank you!