An interview takes 1 to 2 hours. Tests or assessments may take another few hours.
There are structured (fixed questions - easy to compare the candidates), semi-structured and non-structured interviews. Semi-structured interviews are used most. A possible structure could be: introduction; presentation of the company; questions to the applicant (job, education, interests, extra courses, skills, team spirit, etc.); hobbies and non-professional occupations; personal goals; contract negotiations; summary; and next steps.
The atmosphere will be cooperative, open and frank. The ratio between non-professional and professional questions will be half-half. It is important to prove your motivation. The employer wants to know as much as possible about a candidate's motivation, knowledge and skills, but also their personality.
You can ask any questions at the end of the first interview. Questions about salary are usually dealt with during the second interview.