Yes, you can customize the buttons at the top of your Pen Tablet as you would like.
They are called Control buttons because they can be set up to control different aspects of the Pen Tablet.
By default, they are set to (from left to right): Launch Settings panel, Adjust Pressure and Switch Displays.
If you are new to our Pen Tablets, I suggest that you leave the Contol buttons set as they are for the first few weeks. Once you have used and become familiar with your new Pen tablet, then you can look at customizing them to meet your workflow needs better.
 Open the Settings panel to access the Control buttons at the top of your Pen Tablet.
The easiest way to do this is to press the top center-left button and select Pen Tablet from the left navigation column.
 This shows the Control buttons and what they are set to by default.
I selected the Control button on the right, and  you can see from the dropdown menu you have an array of different functions you can choose from to customize that Control button.
** I suggest you leave the top left-center button set to Launch Settings.
This will give you an easy way to access the Settings panel when you want to go in and make updates.