About 4 years after beating my head against the wall trying to learn all about embedded linux builds and reading through yocto docs, I found a course on Udemy titled, "Embedded Linux Step by Step Using Beaglebone Black" It was perfect for walking me through the kernel, file-systems, boot-loaders, etc... It was a bit dated even then and thus required a little leg work to find the proper source versions of linux for the beagle board but I got it all working and cross-compiled a linux distro from scratch for the beagle board, flashed it, booted it and talked to it via serial port. I highly recommend the course.