Once you've got yourself set up you'll need to edit the config file to change the paths to your shader and images. The vertex shader is called "joey.vert" in honour of the person whose tutorials I followed (https://learnopengl.com/) and must not be moved from the shaders folder.
The fragment shader is the one you'll be customising, you have access to the texcoords and sampler uniforms of your images that were specified in the config file. "color" is the variable that is rendered to the screen and is a vec4.
I have just remembered I need to pass in the window dimensions as uniforms. This means things like sobel won't work unless you know the size of your window / image.
Lastly it uses OpenGL 3.3 so make sure your graphics drivers are compatible.
Right... I'm going to make that change...