This is the most critical concept to understand:
For beginners using MAME2003-Plus, Non-Merged sets are highly recommended. You simply drop the ZIP file into your ROMs folder and play. mame2003plus roms
If you are using a frontend like RetroArch (common on PC, Android, and devices like the Anbernic RG351), the directory structure is vital. This is the most critical concept to understand:
: Specifically tuned to achieve full-speed 60 FPS emulation on low-end hardware. The Anatomy of an Arcade Romset and devices like the Anbernic RG351)