Add new programs - what's happening?

I've got an aspire one with Linpus Lite, and I'm totally unfamiliar with Linux. I've done the little hack so that I can use the linux desktop on right click.

Then I followed directions I obtained elsewhere for adding a new program (skype). (works great, btw. Instructions are here: http://www.theacerguy.com/2008/07/25/ge ... spire-one/) This involved using the "add/remove software" feature on the desktop menu.

On clicking add/remove software, the computer connected to the internet for a protracted period of time, and appeared to download an enormous amount of information about all sorts of programs. If I had to guess, it seemed like the computer was downloading some sort of information about every known program. This must have taken 5-6 minutes on a reasonably high speed connection.

My questions are: what exactly is happening when I do this? What is being dowloaded, where is the information coming from, and where is it stored? Do I have to do this every time I install a new program, or is once enough?

 

The items and amount of data downloaded depends on the program.
Some programs will cause a lot of data to be downloaded.

 

It will grab a 'small' file which contains the name of a program, it's description and it's catagory that way you can browse for what ever you want - without it having to refresh and grab more data everytime you want to browse another catagory.