Labelling in github really a useful way to separate and track issues in clean and convenient manner, so is there something similar in fossil ?
You don't have freely assignable tags in Fossil tickets. Instead there is a predefined type dropdown field (with values like defect, documentation, feature request, ...). Since the whole ticketing component in a Fossil repository can be customized by the user it's easy to adapt this to your wishes. You could even create an additional field in your tickets. It depends on what you want to achieve.
Here is the Fossil documentation on how to customize the ticket system.