You submit an application for temporary protection to the employees of the nearest police department or precinct at your place of residence, where soon after your application is approved, you will be issued with a Certificate (identification card) of a foreigner who has been granted temporary protection.
You can also apply for temporary protection online through the application - https://croatia4ukraine.mup.hr/Pages/Zahtjev.
If you are in institutions of collective accommodation of displaced persons, you do not need to go to the police station or headquarters, you can submit an application for temporary protection in the relevant institution by contacting the employee of the Ministry of Internal Affairs on duty or an employee of the station/police headquarters.