Run make and browse to dist/index.html. make sets up hard-links
for most files, so they can be edited without having to run-run
make.
This is what I had to do to build and install Bootstrap under Debian jessie.
Download https://github.com/twbs/bootstrap/archive/v3.0.0.zip and unpack it. Install Debian's nodejs and npm packages (I had to install npm from unstable, but its dependencies came almost exclusively from testing). Create a wrapper script called "node" in your $PATH that invokes /usr/bin/nodejs. This is apparently the legacy name of the nodejs binary and I found that a few packages still used it. Install grunt and Bootstrap dependencies. I did this all locally, since I didn't want npm mucking with my system:
npm install grunt-cli npm install
npm install esprima
Finally, build Bootstrap and copy its output
node_modules/grunt-cli/bin/grunt dist cd .. mv bootstrap-3.0.0/dist/* .