Help Please

I have read through countless articles and posts but I still do not know what a emulator and a ROM is someone please answer my question ;D :) :-\ :'( ??? 8) :o :( ;D :D

An emulator is a program that essentially emulates what ever system it's trying to emulate on your computer.A ROM stands for Read Only Memory (which isn't really true anymore), it's a cartridge based game, like games for all Nintendo consoles up to the Gamecube, Sega Genesis etc.
When you say you're downloading a NDS game, you're saying you're downloading a NDS ROM.ISOs are disc based games like games for the Playstation.

Uh oh, that might take a while to explain, you may want to read this and this.But basically emulator is a program to simulate (and hopefully, surpass) a system in another system while a rom (in this case a NDS rom) is a digital copy of the data stored inside an NDS cartridge. :)

Do i have to download anything for the ROM to play on the NDS

You will need a Flashcart (e.g. CycloDS ) with a micro SD memory card roughly 2GB to 4GB in size. Download the rom and extract it with WinRAR and copy it to the memory card and place it into the flashcart and boot up the DS and hopefully it will load up. This depends on the brand of flashcart you decide on as there is some tweaking that might have to be done for it to run correctly, sometimes they load with no problems at all.

Only the ROMs themselves. Additionally, if you want to play them on your actual NDS system then you need to buy a flash cart such as the Acekard 2.

oh so like the r4i right
a flashcart is like a card but will a slit in the back with a sd micro slot i think

Yes or whatever form of media it uses (commonly the MicroSD). Can be built-in Nand too.