Assignee in Step is the Assignee that will be set to the Jira issue when the Process starts. When you assign users to a task, you give those users responsibility for that particular piece of work. They are the ones who can view issue with the form, potentially complete it, and be accountable for it.
You can assign Step (issue with a form) to:
Only Assignee can fill out the form in Jira issue.
Instruction on how to assign Step
Select the Process Step you want to add an assignee to.
Select the assignee from the drop-down list. You can select one or a few Users or User Groups. This list reflects users and groups assignable to Selected Project – BPM Templates (BPM).
When the Process Starts, all Assignees will receive an email notification that the task is created for them.
If more than one user or group is selected, the system will create a separate issue with this form for every Assignee.