If you are not familiar with what a custom activity type is you can learn more here
Begin in the administration panel and find the Activities section on the left.
Add an activity type, the example here consists of creating a ticket
Next, start building out the custom attributes you want to appear on this ticket activity type.
Above is the custom attribute Severity Level which has drop downs to choose from.
Once all attributes are built go into the Activity Attributes Layout and title the section of this ticket, ticket information
All attributes created will appear on the right-hand side, you can then start dragging each one over to the new section, dividing them by either one column or two.