How to use the orange squeezer?

Excuse me, I'm a bit puzzled about the usage of this orange squeezer. Could you kindly guide me through the process? Do I need to cut the orange into half first before placing it on the squeezer? Or should I just hold the orange whole and squeeze it down? Also, is there a specific angle or technique that I should follow to get the maximum juice out? Lastly, should I clean the squeezer after each use to avoid any bacteria buildup? Thank you for your time and assistance.