I have several of these 'TT Cards' for my kids.
Firstly put the micro sd card in the sd card adapter and format it in your PC. When you go to format please slect restore default settings and then click format. (That is ofcourse if you have a micro sd card? If not a 2gb one will hold about 20 games)
Then open the location that you sd card is E: etc and create a new folder called Games. This is where all the .nds files you would have downloaded will be put.
You then need to drag and drop the latest firmware for the TT card onto the sd card in the PC. You can get i here:
Just download and unzip. If you need it winrar is a free download.
Ok, after you have done all of that you need to take the sd card out of the PC, put it into the tt card, put the tt card into the ds, turn on the DS and let it start up.
If all is done properly you should see a nice TT card menu on the screen!!!
Now turn off DS, remove tt card, take sd card out of tt card, place micro sd card into adapter and then into pc, open sd card location, open games folder and just drag and drop downloaded nds game files there.
Please remember only .nds files can be played on a flash cart of which a tt card is one.
Also look for a ds rom trimmer tool on google. Will make the game a lot smaller so you can get more on the card.
Hope this helps.
Anyproblems please message me back.