Your phone has a touch screen. You can use this in conjunction with the physical buttons on your phone to take advantage of the different features.
This is what your main display will usually look like:

You can see your extension number in the top left corner of the screen. It usually falls between 200-220.
If you hit the more button, you will see more names and a few other buttons. Your phone will change to look more like this:

From this view, you can see all of the touchscreen buttons available to you. All of the buttons with the symbol of a person can also indicate the status of that function. If the person is red, then the function is enabled. If a coworker is on the phone, the icon will turn red by their name. If the system is in night mode, the night mode indicator will turn red.
These are the physical buttons mapped to the button names:
