Chemo, explained by my simple brain, are drugs that are given to you to kill cancer throughout your body. There are many, many different chemo's, so there are many, many different combo's they can come up with depending on what you are fighting. So again, there are various side affects that can occur. It kills the cancer cells, but also kills your good cells and can cause you to become sick very easily because your immune system is shot.
Radiation is treating a very specific area of the body through - well, radiation. Like an x-ray I guess. This is what the machine looks like... a giant kitchen mixer.
This picture is one off the net, but the one that is used here is very similar.
You lay on a table in a specific position to how your treatment has been set up. That is why they put tattoo's on so that they can line you up exactly for your treatment each day. The tech's (I think that is what they are called) set you up, and double check your positions with one another and then they leave the "vault", seriously that is what it is called. It is three walls of cement and there you lie, half naked on a table being fried while everyone else is well out of harm's way. I have told myself that the people who do this job for a living need to be well away from the beams as they do this all day everyday. So it must be safe for me... ya right. But, life saving? (still reading a lot about natural ways to kill cancer) none the less.
Dr. M explained it to us as an extension of the surgery. Just to make sure that they got everything. They are also doing my neck because I have lymph nodes that run up there and still more behind the chest muscle that aren't removed.
That about sums up the difference in my uneducated version. I hope this helps!