BeagleBone Debian Machinekit image
Robert C. Nelson kindly provides a 2-weekly build of a complete Debian with Machinekit image for a BeagleBone Black/White.
Head over to elinux.org/Beagleboard:BeagleBoneBlack_Debian#BBW.2FBBB_.28All_Revs.29_Machinekit and download and install the image on a microSD card and run the image from that, or install the image on the eMMC.
The 3.8 kernel version image is recommended as a starting point.
This uses a xenomai kernel and is pretty much guaranteed to work without any adjustment of configs etc.
There are later rt-preempt 4.x.x kerneled versions of the image available on the same site.
These will require some familiarity with the BBB boot process and the configs to use sucessfully.
For kernels after 3.8 you may need to change the device tree overlay in /boot/uEnv.txt.
https://elinux.org/Beagleboard:BeagleBoneBlack_Debian#Loading_custom_capes has some help on this matter.
Read the posts on the forum covering these images and when they make sense to you, you are probably ready to try the later images :)
Instructions on writing a microSD card can be found here by doing a Google search. There are plenty examples and tutorials around also for writing the image to the eMMC.