Menu: Filter -> Assign Filter…
Drag and drop: see below
Activates the selected Custom filters or a subfilter thereof, if you selected a subnode, so that the logmessage pane displays only logmessages that match this filter.
Note:
A possibly activated Loglevel or time filter may hide additional logmessages, as these filter kinds work additive. See kinds of filters.
Using drag and drop:
You can drag a Custom filter or subfilter from the filterset pane to the logmessage pane.