please help me with nintendo 3Ds?

please help me with nintendo 3Ds?

im planning on getting a nintendo 3DS for christmas, but i cant figure out how it works.
can you download for free 3DS games on to a r4 card and play them in 3D on the nintendo 3DS, like you can on a nintendo DS lite(in 2D obviously)?
or can you download or get games for free another way?
or is it better to get a nintendo DSi or another DS lite?