When you create a new Job, you are prompted to select a Participant type.   Once set for a particular job, it can not be changed.

The only other mandatory fields when defining a Job is the Job Name.

Although not mandatory, it is highly recommended that you define the time-line for the Job by providing date/times for both the Job Starts and Job Ends fields.    

HINT:  It's a good idea to consider how you would like to manage/assign participants to your jobs, when creating the their respective time-lines.   For example, let's assume your event is over three days and one of things you need to do do, is Entry Gate Security. 

A simple approach would be to create a single Job, called Gate Security and the time-line would match the Start and End date/times for your complete event, spanning all three days.   However, when you are assigning resources to this job, it maybe unrealistic to assume every participant would be working the whole three days at this same activity.    

Alternatively, you could create three distinct jobs, representing each shift.  Let's call them Gate Security - Friday, Gate Security - Saturday, and Gate Security - Sunday and then define the respective time-lines for each individual shift.   Now, when you assign resources you are assigning them to each shift.  It will be easier to identify any deficiencies and act accordingly.   Of course, it is possible to assign an individual participant to multiple jobs, so if you did have a participant that was working all three days, then you simply assign them to each jobs/shift.

Furthermore, when you are creating your registration forms, define your availability periods to coincide with the time line you set for your jobs/shifts.   This will make it very easy to manage your resources and find the most appropriate participants for each job.

Two other fields that are not mandatory, but effective in your resource management efforts are: Target & Capacity 

Target - the minimum number of participants that you need to get the job done.

Capacity - the maximum number of participants that you can assign.     Capacity must not exceed the Target.

Both Target & Capacity can be updated if necessary and the various indicators in the Jobs widget will reflect the changes so you can easily identify any surplus or shortcomings.