The process for making hair for Skyrim is pretty much the same as the process for making armor.
You'll need to know the basics of using the Creation Kit. You didn't mention if you knew how to use it or not. If you don't know how to use it then start with the tutorials here: http://tesalliance.org/forums/index.php?/forum/114-creation-kit-basics/
You need Blender 2.49. Set it up according to the instructions on this page: http://niftools.sourceforge.net/wiki/Blender
(You might be able to do it with the most recent Blender, but if you want to use the method that definitely works, then use Blender 2.49.)
You need NifSkope https://github.com/niftools/nifskope/releases
You can follow Hana's armor tutorial to learn the process for making armor. http://tesalliance.org/forums/index.php?/topic/5639-creating-skyrim-armor-in-blender-tutorial-series/
- When it mentions assigning skin partitions (or dismemberment partitions), use BP_HEAD for parts of the hair that disappear when you equip a hat or helmet, then change it to SBP_131_HAIR in NifSkope, and use BP_HEAD2 for parts of the hair that stay visible when you equip a hat or helmet, then change it to SBP_141_LONGHAIR in NifSkope. Most mods just use SBP_131_HAIR, which makes your character look bald when you equip a helmet. It's probably best to do it like that for now, until you get more experience.
- When rigging, if you made the hair at head height, like the way most mods do it, then use the skeleton from a mod. If you made the hair at ground level, like the way vanilla hairs are made, then use the skeleton from a vanilla hair to rig it.
- When editing the NIF in NifSkope, copy the settings from a vanilla hair or a mod hair instead of an armor.
- You add the hair in the Creation Kit by creating a new head part in "Character/Headpart/female/Head Part" for females or "Character/Headpart/male/Head Part" for males. Look at the settings from one of the the other hairs as an example (E.g. HairFemaleNord01). Here's what you need to set:
Give it a unique name and ID.
Make sure that "Playable" is ticked.
Select the gender that the hair is for.
Set "Type" to "Hair"
Under "Model" select the NIF file for the hair.
Leave the "Tri" field blank for now. You don't need it (I'll say more about this later).
You don't need anything under "Extra Parts". This is used if you have multiple meshes that you want to combine into one hair. You probably only have one, so you don't need to put anything here.
Set "ValidRaces" to the desired race. The standard for humans is "HeadPartsHumansandVampires" (Warning: NOT "HeadPartsHumanoidVampires")
That's all you need to set.
Click "OK" to create your new hair record.
Don't bother making TRIs for now. You don't absolutely need to have them. A few of the tutorials I've seen mention using The Corformulator for generating a TRI. This process does not work, because it creates an Oblivion hair TRI file which has different morph names to a Skyrim hair TRI (and is also used for a different purpose). The hair will work perfectly fine without a TRI.