Inputting existing maps into CC3 is just a matter of tracing them. Assuming you have the map as an image, just use "Draw -> Insert file" to insert the image into the drawing. Put it on a sheet near the bottom of the drawing so you can draw on top of it, and start drawing.
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Making sure the bmp layer is the one I am on, I insert the bmp into the map.
I then change layers and sheets as necessary to add a recatangle for the background fill. Ocean or land.
Then add layer and sheet appropriate polygons for the ocean depths, then add land and land contours.
Add symbols and then text.
Go to the bmp layer, hide all and freze lal so only the bmp layer is visible. Delete the bmp from the drawing.
thaw all and show all.
I 'save as' often.
Then save the finished map with the name I am going to use on the web site. Save as a bmp and then use irfanview to resize and save as a png.
This Joining maps tutorial covers basically the same info, but how to join edges so they match.
edit:
Oh, I don't worry about an exact trace, that way leads to madness... :-)