I have marked the tenon (5 in this case) to match to a specific mortise. There are sixteen joints, and they are not all the same dimension. It’s easy to get confused. Here I have evened the cheeks with a sharp chisel. I also have shortened the tenon by about 1/16″ (15mm.) The reason for this is to allow a little space at the bottom of the joint where any excess glue can go. I chamfered the leading edge of the tenon to make it easier to fit into the mortise.
I now go back to corresponding mortise and clean it up so that the tenon fits snugly, but not too tight. If the joint fit is too tight, there is no way for the entrapped air in the mortise to get by the sticky glue. The tenon will be thoroughly and only partially stuck in the mortise. No amount of hammering will drive it all the way into the mortise, nor can it be extracted without drilling a relief hole into the mortise from the side. In the meantime, the glue is drying. Talk about a headache.
There are several websites that cover the fashioning of joints, but the single best book I’ve ever found that covers the making of all joints is Woodworking Techniques: joints and their applications by R. J. DeCristoforo published by Reston Publishing Co., Inc. Reston, Virginia. This book is long out of print, but you can find it on the web for less than $10US. The author was a talented craftsman and prolific writer of how to books.