You will need the Full Write Workflows permission, be an admin on the associated workflow, or a manager on the process to perform this action.
Navigate to the process you want to add the person to and select "Add person to process" under the "Actions" drop down menu in the upper right area.
You can also click on the "Queue" tab and then on the "Add Person" button.
A pop up will appear with the following fields:
Person - search for the person you want to add to the process.
Starting Task - the task they should start in. By default, this is the first task.
When finished, click on the "Add" button to add them to the process. Check "Keep open and add another" if you are adding multiple people to the process.
Note: When viewing the "Queue" tab, you may notice the person was added with a status of "Queued." This means the workflow engine has not moved them into the task yet, but will in the next second or two. You can refresh the table in a couple of seconds to see the row updated to the correct task.
Restrictions
There are some scenarios in which adding a person to a process will not be allowed.
The person cannot currently be going through the process (i.e. has any status besides Done.)
If the person currently has a Done status, the process reentry buffer must have expired for that person before they can be added again (see below).
Of course, if they have never gone through the process, they will always be added. See this article for more information on the process reentry buffer setting.
Helpful Tips
People can also be added to processes automatically by setting a trigger on the process.
You can also set a person to be automatically added to a process based on custom form submissions. This can be based on either the submission itself or based on answers to specific questions.
A person can also be added when they text in to an SMS keyword.