You can learn more about Workflows here. In this post I just want to cover how you would go about attaching a Workflow Process to multiple contacts in bulk.
From your Advanced Search page, after running a search that will include your desired contacts, place checks to the left of the names of those contacts to whom you want to attach your Workflow:
In the example above, I've selected three records to whom I want to attach the Workflow.
My next step would be to click Bulk Actions in the Contact Options menu above my search results:
I would then select Workflow Link:
After clicking Workflow Link, I'll then see the Link Selected Contacts to Workflow modal, where I can then choose from my existing Workflow Processes to attach one of them to these six contact records:
The Workflows available here are those that your database users have established within your CRM - you can learn more about adding Workflows to your database here.
To select a Workflow Process, just click inside the Workflow box, choose your desired Workflow and then click Link to Workflow.
In the above example, once I click Link To Workflow, these three contacts will have the "Beneficiary Change 2016" Workflow attached to their records.