Pipechimp is is an add-on that adds integration features between pipedrive and mailchimp.
Sending the group emails to people would be handled in the Mailchimp email program, not in pipedrive.
The 'professional' and above version of pipedrive allows for group emailing natively within pipedrive nof up to 100 contacts at a time. In that case you would build a filter of the contacts you want to email, apply the filter, select the checkmark to select all contacts in that filter and then a button appears 'send group email'
Group email inside pipedrive:
To my best knowledge Pipechimp is not being actively worked on anymore.
But if you're looking to send bulk emails to Pipedrive segments then I'd recommend giving Outfunnel a go. You could then send email campaigns from Outfunnel with a 2-way Pipedrive sync -- or you could use Outfunnel's app connector feature to sync data between Pipedrive and Mailchimp and send emails from the latter.