Your custom price book is where you can list the prices for items/services that you do not get from a supplier, for example travel time and materials made in shop.
The custom price book can be viewed and edited by clicking Edit Custom Price Book in ⚙ Settings > Price Books:
From here you can see the list of items you have added and their type
(i.e. labour or materials). You can adjust their prices, add new items, and remove unwanted items:
Searching for items
You can search for items by pressing CTRL + F and typing into the box that appears in the top right: