Marco
Hi,

There are some existing types of the notifications options in our system.
So, after the registration users get the Verification and Welcome emails. You can edit the content of these emails via the Admin Area> Settings > Languages section.
Other type of notification these are the notifications about user actions from the actions list on the page My preferences/Email Notifications.
And with the exception of actions from this list above, users can also receive other notifications using the Mass Mailing functionality. See more about the Mass mailing here: https://docs.oxwall.org/user-manual:users:mass-mailing .
Also you can try searching some suitable plugins in our Store. For example this one: http://www.oxwall.org/store/item/234 .

If I misunderstood you,  please provide me more details.

Do you mean like a monthly newsletter?

Where i can find Verification and Welcome emails in language section?

go to your lang section in admin and then do a search for for the words

welcome

verification

you will know it is an email because the text key will have the word email in it. 

Thanks.

WHEN exactly are SENT THESE email (welcome and verification) ?

the welcome is sent after registration and the verification is sent if you have the email verify option checked in admin and after they register.