If you have already handled and dealt with a Customer issue and it's been resolved, the system allows you to archive the information. This is a great way in which to keep the information within the system up-to-date and organised.
There are two ways in which you are able to do this, either from within the Customer Service Ticket attached to an Organisation or a Contact or in the Customer Service Ticket Section (located in Setup & More).
Within a Contact or Organisation Record
Once you are in the Contact or Organisation Record and have clicked on "Service" this will highlight any customer issues that have been logged against that individual or organisation - so click on the Ref number (highlighted below).
This will open the Customer Service Ticket and allow you to archive it by simply pressing "Add to Archive"
Here are some further guides and tutorials that you may find useful:-
How to View you Archived Tickets