While there is potentially a lot of detail in the answer to this question, let's stick with a basic answer to the question, and this should be a good place to start.
Musicians & Gear
To play in online JamKazam sessions, each musician in a session will have a computer, an instrument (and/or their voice if a singer), an audio interface (black hardware device pictured below in between the computer and guitar), a microphone (not pictured below, but needed for singers and to capture audio from acoustic instruments), and a pair of headphones (plugged into the audio interface).
When you play (or sing) music in a JamKazam session, your instrument and/or voice produce analog audio. The analog audio from your instrument and/or voice goes into the audio interface via a cable connected to your instrument or a microphone. The audio interface converts your analog audio into digital audio that a computer can understand and process. The JamKazam application then grabs your digital audio and streams it across the Internet to the computers of the other musicians in your JamKazam session. If there are three total musicians in a session (including you), then JamKazam streams your audio to the two other musicians.
While you are playing/singing, at the same time the other musicians' computers are sending audio streams of the audio of their performances to your computer. Let's stick with the example of three musicians in your session, including you. The JamKazam app running on your computer then takes the two audio streams of the other musicians, plus your audio stream, mixes all three audio streams together, and plays back the total mix of all three musicians out through the audio interface into your headphones.
This audio processing ideally happens so fast that it sounds like you're sitting next to each other, playing in the same room. The degree to which this is possible depends on a number of factors. If you'd like to understand more about the concept of latency in remote music performance, here is a help article that goes into more detail.
In addition to audio, JamKazam supports video in sessions. Video is streamed among musicians just like audio, and each musician's webcam video is displayed within a video window. The format of this video window can be set as desired by each musician in the session.
Interested in learning more? Learn next about "What Is Latency & Why Does It Matter"?