Features and usage are summarized on the homepage.
The script will prompt for confirmation before it does anything:
ruby -e "$(curl -fsS http://gist.github.com/raw/436471/install_homebrew.rb)"
Afterwards, install Xcode.
Indeed, you can. Refer to our complete installation instructions.
Alright then… as long as you know what you are doing:
sudo chown -R $USER /usr/local
curl -Lsf http://github.com/mxcl/homebrew/tarball/master | tar xvz -C/usr/local --strip 1
The wiki is your friend.
I'm Max Howell and I'm a splendid chap.