I've downloaded the glfw source from their site but I don't know where to go from there. I'm on linux opensuse.
You probably have to compile the code and then start using.
From Compiling GLFW you get the information below. After that you may follow the quick-guide
Generating files with the CMake command-line tool To make an in-tree build, enter the root directory of the GLFW source tree (i.e. not the src subdirectory) and run CMake. The current directory is used as target path, while the path provided as an argument is used to find the source tree.
cd <glfw-root-dir>
cmake .
To make an out-of-tree build, make a directory outside of the source tree, enter it and run CMake with the (relative or absolute) path to the root of the source tree as an argument.
mkdir glfw-build
cd glfw-build
cmake <glfw-root-dir>