You can request a substitute while scheduling an absence. Make sure "yes" is checked on the Substitute Required field:Then you can choose if you want to open the job to all available substitute, assign it directly to a specific substitute or choose among your preferred substitutes.

Once your absence has been scheduled and you chose to assign the job directly or to a preferred substitute, you'll be taken to another window where you'll be able to assign the job directly or to a preferred substitute.

On the Direct Assign window, you can click the assign button for the person you had agreed to give the job.

On the preferred substitute window, posting it will send your job based on what you chose on the “Contact Subs” option. If you chose “All at once” it will send the notification to all available substitute, while choosing a delay will send it to the available substitute in order with a specific delay time. Once someone responds to the job, the sending of notification will stop.