Pipechimp setup begins from Pipedrive marketplace where you can find the Pipechimp application.

After you have installed Pipechimp, you are redirected to Pipechimp web application where you see the integration status page.

Go to www.mailchimp.com -> Profile (click your name from upright corner) -> Extras -> API keys. Copy your api key, go back to Pipechimp web application -> API Settings  and paste the MailChimp API key to the API key field. After Pipechimp has verified your API key, you can select the list and click save. The trial period starts at this point.

When you click save, Pipechimp starts to copy your contact persons from Pipedrive to the MailChimp list which you selected. The first copy takes a few seconds to a few tens of minutes, depending on the amount of contact persons in Pipedrive. 

After all contacts have been copied to MailChimp, you can start to use the list for campaigns and the campaign activities are synced back to Pipedrive.