It is common to have a signup form in your own website to get the visitors converted into subscribers of our bulletin boards.
There are different ways to do that, one of them is the own tools that is inside Mailchimp.com
List > Signup forms > Embedded forms
Other way to do, if you have a WordPress website, is to use the plugin by Mailchimp for WordPress. To configure it you will be asked to adjust the API Key to be got in Mailchimp.com:
User > Profile > Extras > API Keys > Create API Key
After we only have to select the list in which we want to create a form, and using the Mailchimp widget put in the place we want to show inside our website.