To create custom page you should follow the next steps:

copy "example.tpl" file to [your_document_name].tpl (for example "aboutus.tpl" - but do not use script reserved names like "withdraw.tpl" or "deposit.tpl")

Change content of the page with your favorite html editor

Upload this file to your server into "tmpl/custom" directory

Check result - https://www.goldcoders.com/demo4/?a=[your_document_name]
Example: https://www.goldcoders.com/demo4/?a=aboutus

Add this link to the top menu (edit "tmpl/logo.tpl" file) or to the left menu (edit "tmpl/left.tpl" file)