The Log window indicates detailed information on important system messages (Log events) including connection statuses and any errors happening in the system with the description.

Each log event is displayed with the following details by columns:

DateThe date when the log happened in the system. 
Log levelThe level (type) of the log happened in the system*. 
AccountThe account which the log happened at.
ExchangeThe exchange which the log happened at.
Event (action)The description of the log happened in the system. 
System messageThe comment of the system on the event happened in the system. 
In some cases, the length of the message may be larger than the width of the “Message” column. In this situation, you can hover your mouse above the message and doubleclick it to be able to read the whole message by scrolling it down. 

* The list of log levels in ProximaTrader terminal:

ALLAll levels including custom levels.
DEBUGDesignates fine-grained informational events that are most useful to debug an application.
INFODesignates informational messages that highlight the progress of the application at coarse-grained level.
WARNDesignates potentially harmful situations.
ERRORDesignates error events that might still allow the application to continue running.
FATALDesignates very severe error events that will presumably lead the application to abort.
OFFThe highest possible rank and is intended to turn off logging.
TRACEDesignates finer-grained informational events than the DEBUG.

Find the detailed instruction on how to use Log window in Working with Log window section.