1) During the Booking Process when creating a Proposal
Under the Settings for the proposal you can click the "Add A Workflow" link.
On the next page you can choose one of your workflows or you can select No Workflow
2) After Booking
You can add, change, or remove a workflow anytime after booking by navigating to the Shoot record and then clicking on the Tasks sidebar menu item. If no workflow is currently assigned, then there will be a button to Assign a New Workflow.
On the next page you can choose a workflow for the shoot. You can also determine whether or not you would like the workflow's scheduled correspondence to be emailed. And you can determine at which Milestone you would like the workflow to start. This is helpful if you have already completed certain tasks within the workflow.
Once you assign a workflow to a shoot (either during the booking process or post-booking) you will be able to see all of the tasks associated with the workflow under the shoot's Tasks sidebar in the Shoot Workflow section.
You can also assign workflows to Events/Appointments on the shoot. Using a wedding as an example, the main shoot (wedding) could have a wedding workflow attached to it. The main shoot's workflow is the Shoot Workflow. The Engagement Session could have its own workflow. And so could the Viewing Session. You simply click on the Event/Appointment under the Tasks sidebar and assign a workflow just as you would for the main shoot. In this way, you could have multiple workflows on a shoot.
If you need to change or remove a workflow from the Shoot, click on the Reconfigure Workflow button. This will allow you to choose a new workflow or select No Workflow. **Note: Selecting a new workflow will abandon all tasks and history associated with the previous workflow!
Note: Modifying a workflow (under Settings > Workflows > Shoot Workflows) will not affect a workflow that is already attached to an existing shoot. To have the modified workflow apply to an existing shoot, you would need to Reconfigure the shoot's workflow as described above.
Check out this article to learn more about Placing Shoot Workflows On Hold.