First interview
Also known as a pre-interview, the first usually begins with a one-on-one interview with a hiring manager. The interviewer typically asks questions about the candidate's qualifications, skills, work history and relevant experience. They also try to determine if a candidate would be a good fit for the company culture. The company may shortlist some candidates after this interview who can proceed to the next round of the interview.
Second interview
After an initial in-person interview, a second interview is usually more in depth and may even be a technical interview. A second interview is to determine whether candidates are genuine contenders for the job and further reduce the pool of candidates. Sometimes it may be additional meetings with the same interviewer, or it can be a day-long meeting with various members of the staff, like executives and supervisors.