Ok, so here's a basic rundown. The most typical material was parchment/vellum, so that's what I'm describing (ignoring the semantic debate between the two terms).

Making Parchment

(1) Get animals to skin (calf/goat/sheep)

(2) Skin animal (flaying)

(3) Soak in water for about a day

(4) Place in lime/alcohol solution for a few days to remove hair and flesh

(5) Rinse in water again for a few days

(6) Attach wet skin to wooden rack and stretch it by taking pebbles, wrapping those pebbles in the edge of the skin, then tying ropes around the pebble/skin, and attaching those ropes to wooden pegs that can be turned and tightened. Like this. The pegs would turn like you would tighten a string on a guitar or violin.

Note: Nails cannot be used to do this because it rips the skin on the rack - Wikipedia is wrong, yo.

(7) Scrape skin with a lunellum to remove whatever is left of the hair and flesh as the skin dries (crescent shaped blade with handles on both sides)

(8) Tighten the pegs as needed

(9) If holes appear in the skin and aren't too big, they can stay, or if the manuscript is not going to be very important the scribe will work around them. Big holes, or skins to be used for important manuscripts, are stitched up using gut or thread. Like dis

(10) The parchment maker continues to scrape the hide to desired thickness. In order to prevent the hides from becoming stiff, he pours hot water onto it to keep it moist until he is done, and so that he does not stretch the hide too much while its dry, which would rip it.

(11) Once it is totally dry, you done son.

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Writing a Manuscript

(1) Parchment is not square, it's whatever shape the animal was, so you have to cut it to whatever size you want.

(2) You have to decide how you want to organize the leaves (pages). Except in Britain, parchment looked different depending on if you look at the hair side of the skin or the flesh side. The flesh side was a little whiter, hair side a little browner. Things look good when they match, so you needed to order your parchment leaves so that flesh side was facing flesh side and hair side was facing hairside.

(3) Decide how many times to fold your parchment. A parchment leaf that makes one page is called a folio. If it makes two pages (one fold) it is a bifolio; four pages (two folds) quarto; eight pages (three folds) octavo. The standard was bifolio.

(3.5) For a bifolio, create a stack of four leaves. The first leaf is flesh side up, the second flesh side down, the third flesh side up and the fourth flesh side down. Now when you fold the parchment in half, The pages go 1. flesh; 2-3 hair; 4-5 flesh; 6-7 hair; 8 flesh. This grouping is called a quire and 8 was the standard number in the Middle Ages.

(4) You want to write straight, so you have to line you paper. You do this by pricking the edges of the leaf with your knife at regular intervals, then drawing a line with plummet (precursor to graphite) or drypoint (scraping a line with your knife).

(4.5) You can do this before or after folding your parchment. If you do it before you only have to mark either side of the leaf. If you do it after, and are doing a bifolio, you have to prick both the outside and inside edges of the parchment - imagine little dots going up and down the outside and inside of the pages of a book outside of the text.

(5) Make your ink!! The most common type of ink was iron-gall ink, which was black, but usually fades to a rust color after 1,000 years. You can google how to make it, but it involves wasps.

(6) Grab yourself a quill or reed pen (quills were better and the preferred feather was from the right flight feathers of a goose because they swooped away from your hand)

(7) Actually start writing. If there are no images, you're set, just go. If there are images, fancy capital letters, etc., you have to leave room for them, or trace an outline to be completed later.

(8) Finish the illustrations and capitals, this is sometimes outsourced to another shop.

(9) Put the quires in order, this is usually organized by marking the bottom right corner of one leaf with the first few words of the one that followed it (no pages numbers until the Renaissance, usually)

(10) Through the middle crease of the quires, sew vertically to hold them together. (this is optional)

(11) Using a small wooden rack that looks kind of like a vice, take all your quires -- in order!! -- grab some strips of leather, or extra parchment, and sew through the folded quires, attaching them together via your strips of leather. Smash together and tighten.

(12) Your leather strips were longer than they needed to be right? Good. Now grab two pieces of wood, a little bigger than the parchment, and make grooves in them that line up with the leather straps. Glue those mamma jammas down.

(13) Cover the whole outside with leather to hide the grooves

(14) Glue the extra on the inside cover.

(15) Glue the first and last sheets of parchment to the inside cover to hide that ugly leather hangover.

(16) Fancy clasps are optional.

Now you've made a book!

The best resource on the subject is Timothy Graham's Introduction to Manuscript Studies. A more immediate resource is here