You can use the warning functionality. Go to automated actions and click on modify using python code. You will see a basic description of the function. There's plenty of youtube videos about this as well.

Hi,

I hope you are asking about how to implement the security mechanisms in odoo, in odoo the security mechanism is implemented using the groups, access rights and the record rules.

A user group is created and the access rights and rules are set to this groups and later this group is assigned to the users, so what user see on his login will be based on the access rights and rules of his user group.

Please see this for information about the same: Security in Odoo - Access Control, Record Rules and Group

Thanks