How to blend two circles of different sizes, so that one end is a smaller circle and the other is a larger one?
Hard to tell from your screen shot exactly what you are trying to accomplish. Do you have an image of what it is you are trying to model so we can see what your goal is?
Maybe something like on the right? I extruded the flat face of the dome with Push/Pull and then scaled the end face to create the taper.
Could also draw a cross section of the whole thing and use Follow Me.
For a shape like that, a cross section of the cut witl the rolled rim and a circle for Follow Me is probably the easiest option.
How about if two circles are not aligned on the same axis, like below?
Again, your screen shot doesn’t provide a lot of information.
Extrude one of the circles with Push/Pull, scale one end face, move the face off center.
Might be a good idea to spend some time learning the fundamentals at learn.sketchup.com
BTW:
Your images show that the model axes are off or the drawing elements are very far from the axes.
Take a look at Dave’s pictures, so the model is more transparent, eloquent and manageable when you draw along / near the axes using their “assistance”. 
Hi,
please go update your profile, there is no sketchup version 10, never was, went from 8 to 2013
it’s in your profile, top right of the forum.
Alas, there is no fundamental course about using the forum and filling in your profile, but anyway, if you need a refresher, you can always consult the SU fundamental
cheers 
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