Hi @ Jessica Marfoldi,
If your projector has a HDMI input, you can connect a Galaxy S9 to it to view what is on the phone’s screen through the projector.
You will need an adapter to connect the phone’s USB-C port to the projector’s HDMI port.
Here’s a https://www.youtube.com/watch?v=WIKrRx6CV5s|video] that explains how to connect the phone to a HDMI input