@duubike said:
For example if i draw a solid cube (attached image 1) and then draw a rectangle on it and pull it out (attached image 2) is it possible to make that into a solid? Or the only way to make it into a solid is to draw the second cube as a seperate solid and then merge them together?
This is correct for the example you describe. The problem is that on a more complex object there may be interior faces, or some other geometry that will cause the operation to not be solid.
Here are a few basic principles that you should know when 3D printing your Sketchup models.