When you click and hold the top button, Cortana opens (or Search opens if Cortana is not set up).
Enter your question on the screen.
Click to open a Quick Note
OneNote is a great way to find, capture, organize, and share information. Click the top button on your pen while your Surface is asleep and you can jot a note or sketch immediately, without unlocking the screen. When you’re using your Surface, click the top button to open OneNote.
Double-click to put a screenshot into a Quick Note
Use your Surface Pen to take a screenshot and copy it to OneNote. Here’s how:
1. Display what you want to copy. It can be a webpage, a photo, or anything else you see on your screen.
2. Double-click the top button on your Surface Pen.
3. Select what you want to capture in the screenshot by dragging the tip of the pen from one corner of the portion you want to capture to the opposite corner. When you lift the pen tip, your selection appears in a new page in OneNote.
Now you can mark up the screenshot with the pen, move it to any of your OneNote notebooks, or share it with others.
Source: Microsoft