Quick Play

What is Quick Play and how do I stop it ?
What is the red line above my wave form and how do I get rid of it ?
I assure you I`m not talking about a STD

Quick Play provides a convenient way to start playback at any time position, simply by clicking on the Timeline.
As with ordinary play, playback may be stopped by clicking the Stop button or pressing the spacebar.
See here for full details: Timeline - Audacity Manual

If it looks like this:

then you have a “locked play region”.
See: https://manual.audacityteam.org/man/transport_menu_play_region.html