Included is an HDMI-to-VGA audio/video adapter, since this projector supports 720 and 1080 HD video via either of the projector's two VGA input ports. As shown in the photos, simply connect your HDMI source to the adapter and connect the provided audio cable from the adapter to the audio-in port on the back of the projector. (As shown in the photos, I have connected a Google TV/Chromecast device (not included) to the adapter. This is a great way to present a large-screen backyard movie without having to run an ethernet cable (assuming your streaming device can connect to a WiFi network). (Note--since HDMI streaming device characteristics vary, adapter compatibility with all devices cannot be guaranteed.) Also included is a USB-C-to-HDMI cable for presenting phone video (if your phone is capable of doing this--not guaranteed).
For permanent home theater installation with multiple HDMI sources, I recommend purchasing a remote-controlled HDMI switch ($15-$25) and attaching that to the included HDMI-to-VGA adapter. Then, simply connect your HDMI source cables to the HDMI switch. You can then change between HDMI sources using the HDMI switch remote. In addition, instead of routing the audio cable from the HDMI-to-VGA adapter to the projector (as shown in the photos), route the cable to a stereo input jack (AUX In, Line In, CD, etc.) on your home theater receiver. (You may need an audio plug adapter/cable to match your receiver's audio input jacks.)