This Video is great for a beginner, to learn some basic techniques in photo compositing.  Though it’s not mentioned in here I also recommend you get used to working at a minimum of 450 dpi at actual size. When your work is printed it will usually be at 300 dpi, so you will be working at a higher resolution. This is standard practice, and means that you work will be reduced in size when it’s finally printed. The reduction will improve the quality.