how about changing the description fields?

[Ami Dudu]

This question is in reference to Atlassian Documentation: Configuring the Issue 

in the details view of an issue there is a description tab, i want to add custom fields there, how do i do that?

[Nic Brough _Adaptavist_]

There is no "description tab", I think you mean you have a panel for the description.  You can't add to that, it's there for the description.  Custom fields will land in the custom field panel, unless they're date or user fields.