the first thing I'll tell you what an emulator:
The emulators are programs that allow you to play video games such as Nintendo or NDS N64 to your PC or mobile phone, or even Nintendo NDS Gameboy Advance. These games are known as ROM.
I wish you a good visit and hope the site will be your expectations. Link 3DS page
Citra 3DS Emulator
I personally tested this famous emulator, the developer of Citra they are serious do not waste time trying but I tell you that many ca bug, you need a good computer started playing
There is already a 3DS emulator, the Citra (citra-emu.org). It is still in development and trial versions are released