You did create the needed relationships, the two tables in the lower left where you link doctor_to_users and spec_to_doc. Those are known as conjunction tables and are used to link the id of a user to the id of a doctor. This table can have none, one or many entries showing the user has no doctors, one doctor, or many doctors.
Same with the specializations. You have a doctor id and a specialization id and link the doctors to specialties. A doctor can have no specialty, one specialty or potentially more than one specialty.
The third part there is going to be setup using a query where you link the doctors to their specialties (using the conjunction table spec_to_doc to link doctors to their specialties) and then link to the day of the week the doctor is scheduled for. This will involve another conjunction table.
The only thing I have to immediately say about your tables are the fields doc_to_usr_id in the users table and spec_to_doc_id in the doctors table should not be there. They are not needed. The primary key of each table is all you need and those are the keys that will be found in the conjunction tables. The user and doctors tables are unaware of the conjunction tables. They just represent a user or a doctor's fields.
Hope that helps you out.