For building get Box2d from: wget https://github.com/erincatto/Box2D/archive/master.zip unzip master.zip cd Box2D-master/Box2D
Then Build it: instructions in building.txt file (instructions also in) https://noz3001.wordpress.com/2011/06/19/2d-game-development-with-opengl-setting-up-box2d/
Or on arch, using AUR:s pacman -S box2d
The SFML lib is not included either: on ubuntu: apt-get install libsfml-dev on arch: pacman -S sfml
Then learn about box2d: http://www.box2d.org/manual.html
Noteworthy is the coordinate systems used and units.
The example can be built with make mainThen run by make run