Thank you for your interest in Aspose.Word.
The easiest way to create tables, insert images as well as any other content is to use the DocumentBuilder class and its methods. Nested tables are supported.
Changing whole document background is not possible programmatically yet, but I will log this as a feature request. In the meantime you can workaround to some extent if you insert an image into a header or footer of the document, the image will serve as a watermark on all pages.
If you download Aspose.Word and install it, it will work in evaluation mode until you supply it with a license. The instllation includes a demo project that creates several documents and shows various techniques including using DocumentBuilder to create tables and insert images.