Ok, I think I see what you are asking. The fact is that there are a lot of different GBA flash cards out there. You can get information for just about all of them (the good ones anyway) from
http://www.gamboy-advance.net.
Each flash card works differently and compatibility between different GBA compatible systems such as the micro and NDS is also an issue. Each flash card works by loading the roms that are stored on it from a menu that appears when you start the GBA system you are using (at least that's what I believe happens). You select the rom and begin playing it like you would the real game.
The way you get the roms onto the flash card depends on the card itself. Most will allow you to drag and drop your rom straight to the the card through My Computer. Others require special software that flashes the card with the roms you choose so that they will play on your GBA system. All of them will require special hardware or cables in order to connect them to your computer and will usually come with this extra stuff. Software however will need to be downloaded from the internet.
I have downloaded the software for this card and tested it using Red Rescue Team and the save patch feature is a problem. Basiclly it will probably cause the same issues as the IPS patches for the emulator does. I would recemmend you choose a different flash card as this one does not appear to support any of the Pokemon game's save type.
What you should be looking for if you want to play Pokemon games (I'm guessing that is why you are looking for a flash card) is one that supports 128KB Flash save (and Real Time Clock for Ruby, Sapphire and Emerald).
Check the link above and click on "Compare Flash Cards" to get an overview of what each card is compatible with. The GBA X-ROM flash card seems to be the most promising for what I believe you plan on doing with it. Here is a link to the info page:
http://gameboy-advance.net/flash_card/gba_X-ROM.htmAs far as DS games, you will have to buy special hardware called Pass-me or something similar (there are several different ones). These devices require an actual DS game to boot with and allow you to run NDS games from a GBA flash card using you NDS system. Most DS games will need to be patched in some way before they are able to run this way and only curtain flash card support booting DS roms even after they are patched. I would suggest you look around a bit first before choosing a flash card for this purpose.
The actual sale sites use secure servers for credit card purchasing so your parents should not worry about someone stealing they're information if they buy this for you. As long as they order from the sites listed for purchasing they should be fine. Don't forget to look for the secure icon (may only show on purchasing pages) at the bottom-right of your browser and make sure there is no spyware on your computer before entering any personal information just to be sure.
Hopfully this answers your questions and I hope everything works out for you. I'm sure one of the 1emu staff might post some extra information that I might not have mentioned that may also be helpful.
I should also note that I do not own a flash card myself so everything I have posted above is based on what I have seen or read. I have done quite a bit of research on this and most of it has been though the site I posted above so check it out for more info and don't rush your choice. I don't know everything about this though as I only did so much research so you might find more info that have not mentioned.