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 from the resulting Bulk Actions modal.
After clicking Workflow Link, I'll then see the Link Selected Contacts to Workflow modal, where I can then choose from my Workflow Templates or Existing Workflow Processes to attach one of them to these three 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 Template, just click inside the Workflow Template box, choose your desired template and then click Link to Workflow.
To select an existing workflow already in progress, click inside the Existing workflow box and make your selection. Then click Link to Workflow.