Hi,
The security in odoo is implemented using Groups, Access Rights and Record Rules. If you open users form view, ie, Settings -> Users & Companies -> Users, you can see a lot of groups visible in the form, the things(modules and records) that the user see will be based what is the groups assigned to him.
Suppose if you take the example of the Sales Module, it has got mainly three groups, in the users form view, you can see, User: Own Documents, User: All Documents and Administrator , so the user will see the sales module only if. any of this group is assigned to him. So if you don't want user to see sales module, you don't to assign any of this group to the user.
If you want users to see all the sale order, you can assign the group, User: All Documents and if user want to see only his own records, you can assign the User: Own Documents group.
For setting default access rights for newly creating user you can choose the method by Mr. Oscar Alca in his answer. Also see the same here: Default Access Rights For Newly Creating User in Odoo
For understand Odoo Security Mechanism: Security in Odoo - Access Control, Record Rules and Group
Thanks