How do I mark this so when there’s update, I’ll have notification?

You have to rate this manga (with the stars) you also have to click already read/reading to receive notifications

You don't have to rate, just click reading and submit it

There are three boxes above the summary.
Click one of them, and when something pop out,
Find submit, and click on it. :)

And when you have messages on a topic or notification, a number will be on the bell above

You'll only get notification for mangas you marked as [now reading] and [already read] . The notification will be send in your notification list on top next to the envelope icon.

*But take note that notification often comes late. So best is to just check the [Last Updates] list while you login. You might miss out on some updates.