Hello,
If you need to create a new web content from an existing structure and template :
1- Step 1:Go to the content & data/web content menu. And click on the plus button to create new web content.
2- Step 2: Click on "More" to show all structures.

Choose the structure that you needed.
3- Step 3:Add a title for your web content
complete the form with your data.

Add save your web content with the "Publish" button.
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About the login page, you can't create new web content with .ftl page because the web content doesn't contain the functionality for the login action. So if you want we can create for you a hook to customize the default login page with the Unify design and functionality.
Regards,
Sabri BEN SALEM