Front pannel, starting from the left.
Input 1, 2, 3 and 4 (female XLR/jack combi ports)
Moving to the right, you'll find four gain pots for ins 1 through 4 respectively.
There are two buttons arranged horizontally above each gain pot. Left is Line/Inst (Line is out, Inst is in) and Pad (in is on).
At the right end of the row of buttons just described, to the right of Input 4's Pad , you'll find a single button to toggle between stereo and mono for hardware monitoring (Stereo is out, Mono is in).
Moving to the right, you'll find two pots aligned vertically. The top pot is Mix (left is hardware monitoring, right is PB (what Behringer call the computer audio). The bottom pot is Main Out.
To the right of those vertically aligned pots you'll find one last button, which is monitor A/B (A is out, B is in).
The last pot on the right is headphones volume, and the headphones socket is directly below it.

Back pannel from left to right (from the perspective of the front of the unit facing yoU, IE, looking over the top):
The first four female jack sockets are arranged in a square. These are inserts for the four inputs.
Top left is 1, bottom left is 2, top right is 3, bottom right is 4.
Next comes the "Main out" section:
Two male XLR sockets aligned horizontally and two female jacks aligned vertically.
The two XLRs are main out left and right respectively, top jack is Left, bottom jack is Right.
Moving to the right, the next four collumns of vertically aligned female jacks and phonos are outputs that provide the same functionality from both socket types. They're arranged thusly:
1L jack, 1L phono
2R jack, 2R phono
3L phono, 3L jack
4R phono, 4R jack
Next is the phantom power 48V switch (left is on from this perspective of looking over the top of the unit).
Directly above the 48V switch is a Kensington lock slot.
Two MIDI dyn ports (in is left, out is right).
USB
DC power

If you've found this description helpful, feel free to buy me a coffee, a house or anything in between at https://paypal.me/ScottChesworth
Spotted something that needs fixing? Hit me up on scottchesworth@gmail.com.
On that, shout out to Danny Noonan for his fastidiousness. Turns out I'm not infallible (yet).