The main location to add/edit contacts and their info is in the Contacts tab.
Here you can add/edit the name, address, contact info, and any internal notes. This contact information is what will display on your invoice in the "Bill To" section.
You can also add/edit clients as you are adding your Matter.
Type in the client's name in the Client field of the Add Matter window.
When done with entering information for the new matter, click Save and the client name will automatically be saved under the contacts section.
If you would like to enter the client's detailed contact information as well, click "Add Client" and complete the fields in the Add Client window.
If the client already exists in your program, just typing the name will change the right button to "Edit Client". You can then edit the information currently stored for that client.
*Note: After saving the new matter, if you need to edit the client name, you would need to go to Contacts > Client Tab > select the client name > click edit.