Newbie here needs help

Hello everyone...I am a true newbie and game ignorant. My 10 year old son is interested in downloading some games to try for his DS.
So I tried to download some of the games but the come in .rar format and I guess I need to convert them to .nds format.
We are using the M3 DS Simply with a micro sd card...does this make sense????
What do ya expect from a middle aged mom ;)!!!!
I am gamer retarded!!!

I managed to find the "search option" here and just figured it out!!! This is awesome. Thank you so much for your timely response.
Oh and I had already figured out how to get the "stuff" to the M3 card.
Thank so very much!!!!
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