You need a valid license in order to operate Avantra. The license is implemented by means of a License file used with the Avantra Master. It basically contains the amount of Systems allowed to manage and an Activation Key binding the license to a Avantra Server instance.
A Log Adapter in Avantra provides log entries of arbitrary log sources as an array of standardized sets of key-value pairs. Log Adapters are used in the LogAdapterCustomCheck in order to monitor the content of log files. Log sources can be either textual log files or the Microsoft Windows EventLog. There are pre-defined read-only Log Adapters for the Windows System Event Log, Oracle Alert Log, DB2 Diagnostics Log etc., but you also can define your own Log Adapters in order to monitor other log resources.
Log files in the context of Avantra are text files recording certain actions in a structured way. There are applications our there that consider dumping an arbitrary amount of unstructured bytes into arbitrary files as logging. You can try to get a grip on these things defining an appropriate Log Adapter, but your mileage may vary.