Step 4: I've recieved my package..
Your package may come with a disc with firmware you need to drop onto the microSD card, but it's best that you go to the manufacturers website and download the latest release. Unzip/rar the file and just dump it all on the microSD card. Remove the card from your computer, insert it into the Flash Card and fire it up to see if it works. If it works, power down an insert back into the computer.
Initially, developers had to program for specific Flash Cards, but after the invention of DLDI, developers program for one and you can DLDI patch it for almost any card. So most homebrew you need to patch with DLDI, which is easily done with Chism's DLDI Patcher (Dynamically Linked Device Interface).
You need to download the patcher here (I recommend Win32 GUI for Windows users) and the suitable patch for your card here. All you then have to do is run dlditool32.exe, select the patch and then select the binary/binaries (.nds/sc.nds/nds.gba is the same as 'binaries').