In addition to this document (Kerio Operator, User Guide), the following documentation goes hand in hand with Kerio Operator:
Besides the documentation, you can also target various issues by referring to:
The context help is built in the product.
Product forum — in this discussion, you can encounter experience and problems of other administrators using the same product. You may find a working solution for your issues here.
Knowledge Base — here you can find a set of articles troubleshooting particular problems.