You can filter a Log by highlight, colour or text.
To enter filter mode click the "Stop" button in the top-right corner.
The shortcuts will display as filter buttons along the top of the Log, along with any additional colours you've manually added to Log entries.
Click on the highlight or colour you want to filter by.
You can filter by text.
You can filter by both text and highlight/colour.
Once you've filtered your log, you might want to copy the entries. See "How do I copy & paste log entries?".
See the Lumi Logs Help Guide for comprehensive information on using Logs.