@zakaria.houssam, welcome to Bubble!
Privacy of data is handled in three major ways (not just in Bubble, but general to programming). At a high level, these are:
- Database Structure: how you store information in relation to a user
- View-level Structure: how you choose to represent information to the user.
- Privacy Roles within the Database: the privileges that a user must have in order to access specific data and under what conditions
As you’re starting to build, you want to focus on database structure. Specifically, since Bubble is based around the concept of a relational database (ex. you have a table of users and you have a list of to do list items), you may create a field in the database on the “User” type called “owned_to_do_items”, which is a list of To Do items.
Next, you structure your view-level. For instance, you draw a repeating group on the page with the content type of “To Do items” and you set the data source to "Current User’s owned to_do_items, which gives you access to that specific list of things you’ve associated with that user.
Finally, you may construct a role from the Data > Privacy tab where you set up a few privacy roles. Specifically, on the “To Do items”, you set it up to restrict so that only the current user can see those to dos. You could use a rule like “This To Do’s creator is Current User” and that will restrict access to only those who match the criteria.
These concepts may seem a bit abstract at first, but the more you build, the more readily it’ll come to you.
As well, I cover these sort of concepts on LearnTo if you’d like to explore further.