Skype for Business (Lync) meetings will often have several attendees (up to 250). To eliminate background noises, it may be useful to mute yourself when you are not speaking.
If you are attending a Skype Meeting using a computer, press the Windows logo key and the F4 key at the same time to mute and un-mute your audio.
For other keyboard shortcuts, see Microsoft documentation Keyboard shortcuts for Skype for Business.
If you are using a phone for your audio, press *1 on the phone's dial pad to hear command options.