Help

I'm new to this so i'm a bit lost. I want to download Pokemon Diamond from this site, but what do I need to play it, in terms of emulators.

You'll need a DS with a flash card like R4 (recommended) OR...No$GBA: http://www.emulator-zone.com/doc.php/nds/There's another big thread on getting Diamond/Pearl working on No$GBA.
https://www.romulation.org/forum/index.php/topic,567.0.html