This project is no longer actively supported. The last time I got SPAN to work was in 2014, and those devices were running Android Jelly Bean. I have no idea if the technique we used is still relevant on modern Android devices. You may want to consider looking into Bluetooth Mesh.
I don't have a complete tutorial to share with you. At its core, our technique relied on making a kernel modification to enable ad-hoc mode:
https://github.com/ProjectSPAN/android_kernel_samsung_smdk4412/commit/8fa45142b269a6c0870083846c045f02abad869f
If you have any specific questions, I will try to answer them.