From time to time, to the right of the column listing the topics titles, you will see some blue or red flags.

If you click on them, you will get back to the last message of the topic that you have read
Those flags make it easy to follow an active topic. You will not need to browse pages to continue your reading.
The two colours (blue and red) are used to make two types of messages.
Blue is used for the topics in which you participated
Red is used for topics that you have been reading but not participated yet.
Important : There is a limited number of flags. For this reasons, older topics that you have been reading might not carry a flag anymore. We advise you to delete useless flags to be able to keep track of older messages ( how to delete flags?)