Auto Number is a simple feature that generates a part number when creating a new part. You don't need to use Auto Number if you don't want to. You can always just type in whatever part number you like.
Auto Number uses a numerical value which increments each time you use it to create a new part. By default this number starts at 100001, though you can change the starting value (as we will see below).
When creating a new part, a button is available besides the part number field. Click this button and a number value will be populated into the 'Part Number' field.
Feel free to click this button and give it a try. You can change it afterwards. The "Auto Number" number will not even get incremented unless you actually create the part using the generated number.
Change The Starting Value For Auto Number
In the Setting page scroll down until you see the 'Auto Number' section. Here the current number being used for the Auto Number feature is shown. You can set this value to any numerical value and click 'UPDATE'. When creating a new part, this value will increment until the next available Part Number is found.