Echo in Zoom happens when your microphone picks up the sound coming from your speakers, creating a feedback loop. The simplest fix is to use headphones — this physically prevents your mic from hearing the speaker output. If you can't use headphones, lower your speaker volume, move the mic away from the speakers, and make sure only one person in the room has Zoom's audio active (joining from multiple devices in the same room causes echo). In Zoom, go to Settings > Audio and check "Automatically adjust microphone volume" and make sure echo cancellation is enabled. If the echo is on the other person's end, ask them to use headphones or mute when not speaking.