So I created my main user owncloud and I set with mysql database settings created earlier ....
Now the question is:
if I create a new user (clearly this time when I'm going to create will not be able to set a mysql database) this user will use the main user of my database? there is a way to also give the user the secondary own database?
so that if in the future you'll want to move the user at the other platform I have to copy a single databse
No, there is only one central database for your owncloud setup. You could setup different ownclouds if the users or user groups are very different and you want to separate them (you can still use federated cloud sharing to allow sharing with each other).
I don't know if it is possible to change this behavior in owncloud. I could imagine that you put a feature request that allows users to export their data together with all meta data that allow the migration into a different owncloud setup.
It would be useful to separate the user database ... even during backup...
That would require major changes in the database design. That's nothing quickly done and I'm not sure if there are drawbacks regarding the overall performance @DeepDiver1975
help me pleaseeeeeeeeee
It is currently not possible. Migration strategies for users/groups are worked on, but not yet ready. You are more then welcome to participate in the development.
then the data of other users are transferred to your database entered during the installation, right?
Yes. Of course you can do several instanes each with their own database and then use federated sharing between those ...
In the sense that each user has its own database but that are all dependent main database?