Go to the Subscribers page and enter the manually created list you'd like the form to point to (that is, which list you want people signing up through the form to be added to).

Click on the blue 'Get Embed Form' button. 

You will then be presented with various settings for both sign up options and design customization.

The Double Opt-In & GDPR Settings gives you the option of requiring people to double opt-in when signing up and whether you want to include GDPR relevant information. 

The Sign Up Form Settings lets you decide what information people provide when signing up (such as first and last names) and whether you want to require people to provide this information when signing up. You can also add your own questions by clicking on the '+ Add field' link. (Collecting the email address cannot be disabled nor made optional.)

The Success Page lets you decide where you want to direct people after successfully signing up to your email list. If you have a dedicated page confirming that someone has successfully signed up, this is where to add its URL. Note: If you leave this field blank, people will instead be redirected back to the signup form, so it's best to include your homepage if you don't have a dedicated success page.

The Embedded Form Design section gives you various options for how your sign-up form will appear.

The Embedded HTML Code section gives you the HTML code to add to your site to insert the sign up form. Simply copy and paste this code into your store's site code where you'd like it to appear.