If you do not know KDF9 click here.
If you need a Usercode refresher course, the original manual can be seen on-line here. It was superseded in 1969 by an extensively revised version, which is available in scanned form here. This almost certainly post-dates the software that is available here. The older manual has a convenient contents page with hot links, and is probably a better match for the software available here.
Although the version of Usercode that has survived, is the paper tape version (KAA01PT), It has been fronted here by a pre-processor that takes Algol Basic Symbols so as to be consistent in its use of current character codes with the implementation of Algol 60, as described here.