One was is to connect it via HDMI. You'll need a long cable, but it works perfectly! The thing to know about this method is that you will probably have to go into the display settings once you plug it in and switch it from "Extending" to "Mirroring."
Another way is to leave your teacher computer plugged in to your projector - this is my favorite way! You will need to download the "Google Cast for Education" extension/app for Chrome on your computer. When you're ready to project the Chromebook, click on that icon and give your computer a name (whatever you want). If you have your classes set up in Classroom, you can go ahead and add/invite them as a whole group! Once that is done, go to the 3 vertical dots on the right side of the Google Bar on the Chromebook. When you click on it, about halfway down the list you will see the option to "Cast." Hopefully, from the Chromebook, you will see the name you gave your computer. Just click "Cast" and BOOM! Like magic!