Desktop version (Mac or PC) - https://www.webex.com/downloads.html
You can also download the phone app from your handset's app store.
Background noise can be distracting to other participants.
Headphones are good. They will let you hear other speakers without your mic picking up the sound. Headsets (like apple earbuds) with a mic are even better!
Hover over a participant's picture, and you'll be able to mute them.
Publicly posting a meeting link means anyone with the link can join up!