I’m doing some basic modeling, just making a chair as an experiment to teach myself blender and building up my confidence towards something more ambitious. I’m noticing in a couple instances that multiple vertices appear in the same place. I’m using extrusions, loop cuts and a mirror modifier. I’m also having trouble with loop cuts with some extrusions, any suggestions?
Hello 9jack9,
I believe I know what the problem is here. I think the problem here is the loop cuts.
I am presuming one of the things you have used Subdivision Surface to achieve some rounded smooth effect on your model. You then probably used the Loop Cuts to the control the roundness. Now if you Loop Cut twice in the same area you will have one vertices on top of the other, do this a few more times then you will have several vertices on top of each other. This really does become problematic and you start to loose control over the model. Unfortunately as far as I know there is no one answer to give you to avoid this, it all boils down to practice and thinking in advance what steps to take before starting the model. If I am correct about the Loop Cuts being the problem to having multiple vertices in the same place then at least you are now aware of what is causing it. Hopefully this will help in some way or another.
You need to watch out for how many times you extrude(E key) the same spot without moving those verts. Right clicking doesn’t cancel that extrusion, use grab(G key) or scale(S key) afterwards.
To solve overlapping verts go into Edit Mode > select all verts(A key) > press T to get the left hand panel > click on “Remove Doubles”.
Happy Blending
welcome to the community!
if you want to have control over the sharpness of your edges with the subsurf modifier on, use shift+e and then move the mouse to crease it. try to not use loop cuts for that.
tip: use alt+rmb to select a loop. it helps alot in replacing the loop cut
hope it helps 
Thank you all for the advice and ebb for the simple way to solve the existing problem, i’d been doing it manually before! You were all a lot of help, thanks!