i'm new please help

hi everyone, just to start I am not comp savvy at all so be warned lol. anyhoo I've got myself an r4 card which I got someone else to set up for me as I have no idea how to do it, right so can anyone help me to actually put games onto my card because i download them from this site to my desk top then drag them to my SD card which is on my desktop titled no name I then put my SD card into my r4 card into my DS and I go to multimedia an find my game and get a msg saying...... not support ext.RAR or i try open it through game and then get a message saying ........ error this types of files currently not allowed to operate. I do have an apple mac laptop if that makes a difference..... please help as I'm so confused.
kim

you need to use stuffit expander or a similar program to extract the .nds file from within the .rar file.

and how would I do this like I said not very good with comps I know the on and off button and how to get onto the internet and put music on my ipod and thats it so if you could give me a dummies guide on how to do that i would be really grateful.

Install it, and get the menu or whatever on the .rar file, there should be an extract button of some sort. Sorry I don't really know how Macs work.