CiviCRM Community Forums (archive)

Obviously you can create a custom field in CiviCRM. These custom fields are automatically added to the form inline or in a separate tab. If you want the field to appear somewhere else on the form you can use jQuery to place it somewhere else using a extra.tpl as described here:
http://book.civicrm.org/developer/current/techniques/templates/

No problem, been there too :-)

Sorry to ask I'm still in the learning process.

You can not automatically add fields to existing tabs, that is right. You could add fields to an existing tab programmatically using a civicrm hook. You can find more details on hook in the Developer Guide too.

I send you a link to the template chapter of the Developer Guide. I would not recommend you set up a complete frontend page. If for example you want to add something to the Demographics tab, you first check what template is used. The Developer Guide will tell you how to find that, but it will be CRM/Contact/Form/Edit/Demographics.tpl. You then set up a folder for customized templates and add that to the CiviCRM settings. So CiviCRM knows where your customized templates are.
You then create a new file in your folder using the path, so it will be CRM/Contact/Form/Edit/Demographics.extra.tpl. In that extra template all you do is pick up the custom field using the id or class, and move it to the demographics tab using jQuery? The rest of the template remains intact, as the .extra.tpl is simply added at the end of the core template file.

Does that make sense?

Good luck!