Sessions? Tracks? Isobuster?

i'm a newbie when it comes to burning files to a cd-rw. I wonder if
someone can explain to me in layman terms as I am confused by what I
see. My first attempt was to copy 7 graphic files to a blank disk. It
went smoothly. I went to windows Explorer in XP and viewed those files.
Then I added some more files, btw this is done with XP's cd burning
program. I have bundled Nero, but have not installed it yet. Now, a
while back, I came across a small program called Isobuster and d/l it.
When I went back to explorer to see if the added files were shown, they
weren't. At desperation, I opened Isobuster and this is what I saw. The
title of my burner and then under it an icon saying "CDRW with a plus
sign. Opened the plus sign and it says "Session 1, under it Session 2,
then Track 01 under session 1 and a red and blue box, both showing the
date that I had done the burning. Whn I click on the red box, I see
those original 7 files. When I click on the blue box, the same thing
only in capital letters. Then below that is Session 2, with the same
icons..red and blue, on Track 2, with the same dates. When i open each
box, not only do I see the original 7, but the ones that I had added.
So what does this all mean? Why doesn't windows explorer show all
files? Is there a duplication problem here? If so, can I delete the
first session that only showed the original 7? Is this normal when one
continues to write to this disk at different times, that I would get
numerous sessions and duplications? Isobuster won't answer unless I buy
their program. I would, but I want to understand it first. Please do
not recommend me to some of those cd forums where they have FAQ's, I
tried that and did not find anything in regard to my situation. If i
delete session 1, does session 2 becomes 1? Sorry this is a bit long
for a thread, but i wanted to make myself clear as to what I was
witnessing. I thank you for your time...and Suggestions?