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 run a search that yielded 99 records (only partial results are displayed in the screenshot) — I then selected six of those records to whom I want to attach the Workflow.
My next step would be to click Options in the Result Options widget to the right of my search results and then to select Bulk Workflow Assignment from that menu:
After clicking Bulk Workflow Assignment, I'll then see the Attach New Workflow dialog, where I can add 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 the arrows in the Process box, click your desired Workflow Process, choose a Start and Due Date, choose a Default Owner for the Workflow and then click Attach Workflow Process:
In the above example, once you click Attach Workflow Process, these six contacts will have the "Client Process _ On Board Simple" Workflow Process attached to their records, with Workflow Steps for each of them showing up in the Reminders section of your Dashboard on the applicable date. In this instance you've also indicated to use the Default Owner for the Workflow Steps in this process — you do have the option to select another database user here, though they would be responsible for all Workflow Steps, even if your Workflow Process Template has multiple database users responsible for the various Steps within the Process.
As you can probably see, it's a quick and easy method to set up reminders for a predefined set of Workflow Steps for multiple clients at one time.