These are the instructions if you just want to follow the latest Sage Notebook source, but you don’t need to do any development for now.
The steps are:
From the command line:
git clone git://github.com/sagemath/sagenb.git
You now have a copy of the code tree in the new sagenb directory.
From time to time you may want to pull down the latest code. Do this with:
cd sagenb git pull
The tree in sagenb will now have the latest changes from the initial repository.