This seems like it should be simple, but the process is not working for me, using X1.  I punched in a new part of a vocal and wound up with both the old punched part and the new part playing back.  I am trying to replace the old part of the original layer with the new part in the second layer.  I have tried the Mute tool, but it only seems to work if placed at the bottom of the whole track, not at the bottom of the upper layer, which is the part I want to mute.  So it only lets me mute the part I want to keep.
 
So how can I play back the track with the original punched-in part muted and replaced with the newly recorded part (it is only one measure)?       Thanks.

This is how I do it: Split the original clip at the beginning of the part you want to replace.  Split it again at the end.  Mute the new clip that you just created.
 
I don't remember the default shortcut, but I have assigned the clip mute function to the letter 'm' and to a user button on my control surface.  I use it tons.  It's especially useful when trying to decide which one of multiple takes you want to use.  Mute one clip, select two clips, and every time you hit 'm' it swaps which one is playing back.  This is also a great way to audition edits before you go through with actually making them.
 
If you have a track with a lot of takes, mute all of the clips but one, and then keep two selected - use your current favorite and alternate the selection until you find a new favorite.  Quick and easy switching between takes in real time.
 
Seth
 
P.S.  This may not answer your question about the Mute Tool in particular.  Truth is, I've never used it.  I just use the clip mute shortcut described above.

IIRC The mute tool works like this:
if you want to mute a section of an audio clip click and drag the tool on the lower half of the clip. If you decide to un-mute click and drag on the top half of the clip.

Oh I forgot to mention that if you hold the ctrl key down an click and drag over a section it will mute all other lanes. This comes in handy if you have lots of takes and want to listen to a section of each to decide which you like best.
 

duplicate
 
 

Here is a video by FBB using the mute tool comping layers http://www.youtube.com/watch?v=teGGxrYGvO8

Thanks for responses.  Regarding how to use the must tool, I think I understand but have not been able to make it work.  I wonder if that could be because I am working with V-Vocal clips?
 
Some things I don't understand:
1.  Why do I have 2 waveforms on each of my layers.  Is that just an indication of stereo?
2.  Why can't I play two layers at once?  If I Solo one layer, it will automatically Mute the other one.  I need a way to solo both at the same time.
The fact that I have 2 waveforms for each layer, means that I have a section above and below each waveform, a total of 4 sections.  If I mute by scrolling in the lowest section, it seem I have difficulty un-muting it because if I scroll in the upper layer, it does not relate to the lower waveform which is where I muted.
 
By the way, I did get my song finished but I had to use separate tracks rather than separate layers.  But I will follow through on some of the suggestions, such as checking out the instructional video.
 
I have not installed X2 yet.  Does all this become easier with Take Lanes?
 
But does anybody have a clue as to how I was messing up using the layers?   Thanks.
 

I would suggest that you modify your work flow. Do the comping and choose the best parts of each take. Then if you still need to use v-vocal bounce the now edited track of take lanes to a new track and do the v-vocal editing on that track.
 
You should read up and watch videos on the use of v-vocal as well. When you create a v-vocal clip it makes a copy for you to work with and mutes the original. This is a nice safety net in case you need to revert to the original clip.
 
Yes 2 waveforms is because it is a stereo clip. 
 
If you really want to have more than one layer playing back at a time I would suggest moving or copying clips to new tracks for better control.
 
The solo lane function is working as it is designed. If you want to have more than one layer/lane playback at the same time you will need to mute all the ones you do not want to hear instead of using the solo button.