I have a problem again, I have designed my piece of furniture and have it in the layout bit. But i have quite a few odd lines and marks on the drawing! In sketchup i can’t erase them at all! I have attached a screenshot of the marks.
The dimensions and construction points are in groups or components? If so, you should edit the Group/component and will be able to delete the unwanted parts.
Your image shows some guide points (little crosses) with “tails”, that is, dotted lines back to the reference point they were created from. The tails are not real geometry and can not be selected or deleted by themselves. They will go away if you delete their associated guide points. You can delete all guides from the model via Edit->Delete Guides.
To answer your other question, you edit a component either by double-clicking it or by right-clicking and choosing “Edit Component”.
The best way to work this is to create scenes in SketchUp for the different views you want in your LO project. Then create the appropriate viewports in LO.