2. Connect the Transflash/microSD card to your computer. The R4 comes with a microSD to USB adapter which is very nice. If you have a memory card reader, use the SD adapter that comes with most microSD cards. In a pinch, put the memory card in a compatible phone and connect the phone to the computer.
You may need to format your microSD memory card in FAT32 : Right-click on the microSD memory card in your computer and select format then choose FAT32
3. Open the firmware file, should be Language-Version.zip. Unpack the contents of this archive to the root directory of your microSD card.
4. Verify that you have done everything right. That should be all it takes. Remove whatever game may be in your DS' Slot-1, insert the game card (R4,DSTT), and insert the microSD card into the game card (R4,DSTT). There is only one way it can go, and it will most likely be the way you don't expect. It does not matter in what order you do this - you could also put the microSD card into the game card (R4,DSTT) and then put the game card (R4,DSTT) in the DS. (A clever individual can remove the microSD card from the game card (R4,DSTT) while the game card (R4,DSTT) is in the DS, but it's a tight area.)
5. Turn the DS on. You should get the safety warning, but before you get a chance to touch the screen to confirm, the game card (R4,DSTT) should take over. The default DS menu, if it was enabled (it is by default), will be bypassed, and the game card (R4,DSTT) menu will load. You will get three choices. The first one, Game, will allow you to load a .NDS file (a DS ROM, or a homebrew application - .NDS is to your DS what .EXE is to your Windows computer). The second one, Media, will allow you to play multimedia - music, video, text - using the Moonshell OS. The third one, Slot-2, will allow you to boot a Slot-2 (Game Boy Advance) game.
6. Get some good homebrew games !