To then use the files, you use
open to read 1, "media.pak"
read fileblock 1, "media.bmp"
which will create the file media.bmp from the data in the .pak file. However, if you're going to extract files from a fileblock, you have to remember the order that you wrote the in. For example, if you wrote 3 files to a fileblock, "media.bmp" first, then "picture.bmp", then "music.mp3", read fileblock is going to go through it in the same order, so the first time you use read fileblock you'll get "media.bmp"
Whatever I did I didn't do it!