Question on correcting mistakes

I have Audacity 3.3. I have a couple of questions about correcting mistakes.

  1. When recording a guitar piece and I make a mistake in a section. How can I highlight the mistake and take it out, so I can go back over that section and record the section again.
  2. If I have a situation where I bump the microphone or there is a sound outside my studio while recording my guitar and I want to take out the sound without moving the rest of the track, can I just reduce the volume in that section somehow?