The Sofer, or scribe, writes on scrolls made from animal hide. It is important that the hide comes from a kosher species of animal, although not necessarily kosherly killed, and is thus very clean (free from blemish). The sofer writes on individual pieces of scroll which are then sewn together. This is because there is rarely rubbing out - one mistake and the whole thing is thrown away. Thus, a small parchment of, say, a few thousand words, is much easier to discard of than the last few years of the Five Books in totality, minus three words! More relevant, perhaps, is that there does not exist an animal from which 50 metres or so of parchment could be extracted, so sheets have to be sewn together.
Truthfully, the parchment isn't thrown away, but is buried in a ceremony. This is because the segment is like to contain the name of G-d, which is never to be thrown away, and is hence placed in a capsule where it ages (the scrolls themselves also carry great importance and should thus be cared for anyway).
Once the segments have all been sewn together, winders must be added. There are two winders, or rollers, around which the scroll is wrapped. Before any section is read, the scroll is rolled into the right place.
Once the rollers have been added, a Sefer Torah scroll is truly born.
To protect the scroll from damage, it is usually placed in a cover, with a breastplate on it to remind us of the beastplates worn by the Cohanim, the priests, in days gone by. There is also a Yod, or hand, which is used as a pointer when reading the Sefer Torah, as you are not meant to touch the parchment.
Every Jew is commanded to write a scroll once in their life. Whether through an inability to complete such a task, or through sheer laziness or lack of will, most people commission a Sofer to write the scroll for them. The Sofer will leave the least word, or maybe even the last letter of the last word blank, and the person commissioning him will traditionally fill it in.