This page explains the concept of Jobs. For a list of jobs, see Category:Jobs
Jobs are aquired and practiced for the purpose of completing various tasks such as crafting or collecting resources.
Jobs are obtained by visiting the associated Jobs Tutor. For example, Luia in Nightfall Citadel will teach you the job called Alchemist. You can have multiple jobs at once. While the requirements for obtaining a job differ for each job, they all require that you have at least one job point.
Job Points are used to apply for a jobs. They are obtained by completing main quests. If you do not have any job points, you cannot apply for a job. You can 'freeze' a job to free up a job point so that you can spend it on another job.
Freezing a job means you no longer get any exp for that job but you can still use the skills from that job. For example, if you freeze Botany at rank 9, you can still pick plants that require Botany rank 9, but doing so will not grant any exp and you will not reach rank 10 untill you un-freeze the job.
Freezing a job requires a certain item (Memory fruit?)