what is a rar file it doesnt work on my ds

i have downloaded 100 classic books from this website and it wont play on my ds
i have an orginal ds alredy have games on it and it works
the card i am using is a ezflashv plus and the file came up a .rar how do i play it cause all the other are .ds thank you

You need winrar or 7zip to extract, its compressed to save space and bandwidth

Read this.

I have the WinRAR install file if you want it! ^__^It also works for R4 as well!

Winrar is a free download on most websites, it unpacks the files