These packs are not designed to be actually used but rather as an example to base your own ones on.
Keep in mind that this repository might not always be up to date.
Start here
Have a look at the Minecraft Wiki.
Installing them
Creating them
Make sure you understand the concept of namespaces. Only use the "vampirism" one if you want to override something, otherwise use your own namespace.
A modified vampire skill tree. Removing some branches and adding some alternatives.
Adding new bloodvalues and overrides existing values