I want to be able to add some extra info to users like :-
1.is user banned(can login but have limited access) and for how long
2.all posts that user posted
3.notification center(ex user “Z” answered your question)( new post from Teacher “X” )
----Do I have to make another table for that purpose or I can add to users table.?
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I know how to send notification to users but how am I going to trigger notification if some action happens (like another user react to his post or one of his following user posted something)
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sorry for asking alot recently 
Here’s a blog post with a video that explores an almost identical question:
https://backendless.com/feature-128-run-custom-server-code-when-data-objects-change/
thanks that was super useful but it brings to my mind more questions 
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What is Custom timer (scheduled task) execution frequency? is it how each task has to wait after the last task executed?can I pay to decrease it or I have to switch plans?
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And the another part of the question? about adding more info about users table?
Execution frequency is how often the background task runs. The most frequent schedule would be once a day, however, you can create more than one background task and that way you can have more background jobs running during the day.
As for adding more info about users table, you should be able to do it using related objects.
Thanks a lot Mark
.I can’t edit users table in console it says that it must be done by user properties
Exactly. Have you thought of clicking that link? 
http://support.backendless.com/public/attachments/b4d3aed5b372ce0c29d9f2590917ba3e.jpg</img>
Oh man sorry I didn’t notice .
I should have a rest first :"D