You can add as many custom fields as you need to each panel you have already created. Or, of course, you can create new panels.
Add another custom field to the created panel via CRM Settings. Again, this only applies to administrators :-)
Click your name in the upper right corner ► Settings ► Add-ons ► Create custom fields ► Edit settings.
Select the type of record to which you want to add an custom field.
Click the Create New Field button.
Select a field format, such as a number.
Click the drop-down box next to the panel name and select the panel where you want to add the new field.
Type a name for the new custom field and click Save.
If you want to create a completely new panel, click the new panel name button.
You can change the order within the panel by creating custom fields. Just move the mouse over the grey dots at the beginning of the line of each item (the arrow changes to a cross) and drag the mouse to rearrange them.
In the Phone Calls activity detail, the new panel will look like this: