Today I have an example of one of the creative tools in photography, Depth of Field aka the F-Stop setting. The best way to learn how to use this is to well, do it! Here is an example of two photos of the same subject the first shot at F4.o and the second at F32 both shot using a Canon 100mm Lens.
If you are new to photography or not comfortable with using your camera in Manual Mode use the AV Setting and play with different F-Stop Numbers. Look at your images and the effect of each F-Stop setting. Once you learn this you will start to not even think about the technical stuff and simply know what F-Stop setting to choose to get your photos story across to the viewer.