First, you have to create a job application profile

Second, apply directly for the IRCC inventory postings

But before applying for a job, first, understand job requirements and apply for a vacancy that matches your skills

Check inventory is the best way to find advertised jobs and apply for jobs that match your skill set

If you are a newcomer or a fresh graduate student, you can join IRCC's other programs:

Federal Internship for newcomers program

Student and graduate opportunities

For more info