Go look at the pictures in the first post of this thread. I had to replace a large section of the floor and some wall structure as well.
This is a medium job for someone with some construction experience but maybe too much for a novice. You need to tear out everything that is wet/rotten or moldy. Pay attention and take lots of pictures. Draw out how the construction looks on graph paper and take measurements. Then replace all the rotten framing, put some plywood back down and I bought some random tiles from home depot to replace the linoleum I had to cut away.
The floor wasn't too hard for me, I had it all apart, replaced and sealed back up in a weekend but I have a pretty good wood shop with a radial arm saw, table saw etc. It's all built with common wood that looks like 2x2's but is actually a little bigger. I used my table saw to cut 2x4s down to the correct size for repair.
You may need to remove some of the bottom rows of aluminum siding to get access to the wall studs that may have been damaged. I rebuilt everying on mine with western red cedar, it's a lot more expensive but it resists rot and lasts longer in the elements than spruce/pine/fir.
Mine was caused by a leaky hot water tank, you would do well to check to see if yours is leaking.
JayArr