MailBluster can be connected to your Website Forms using these two ways:
1. Using MailBluster developer API (https://app.mailbluster.com/api-doc).
You need to customize Shopify to send the lead information to MailBluster using the developer API when a customer signs up to the Shopify store. Technical knowledge is required to use the MailBluster Developer API.
2. Using MailBluster WordPress Plugin (https://wordpress.org/plugins/mailbluster4wp).
If your app/website is built using WordPress, you can use MailBluster WordPress plugin to create a subscribe form and add it to your page/post. WordPress Plugin for MailBluster allows the site visitors to become subscribers through a subscribe form which will automatically add them to the MailBluster mailing list without doing anything manually.