This thang is for holding an Arduino Mega / Mega 2560 / Keyes MEGA 2560 Plus - or anything else compatible with that footprint - along with a 400 point breadboard such as the BusBoard BB400 or similar.
It should also fit an Arduino UNO!
The board should friction fit onto the pegs, and you should use your breadboard's sticky back to adhere it to the part.
The station is designed for a 400 point breadboard, but there's no reason you couldn't stick any size of breadboard on there really!
Make sure your bed adhesion is good because this is a relatively large, flat print.
Here is the OnShape document for you to fork and tweak to your heart's content: https://cad.onshape.com/documents/52b234af72c770f4b449169c/w/b143c167bf3ae721f87ee0c5/e/af362b0c3621b749cd6c909c