Whilst AF is very effective, there are occasions when you may want to experiment with your focus point.
For example, when photographing landscapes, focusing about one-third of the way into the subject can maximise depth-of-field (the area behind and in front of the point of focus that appears sharp).
You can do this by selecting the centre AF Point and positioning it over an appropriate area of the subject. Partially depress the shutter button to lock the focus before recomposing the image, but you will need to refocus for each shot.
If you plan to take several images of the landscape, perhaps with different exposure settings, manual focusing is the answer. There is a small switch on the side of the lens which can be moved from 'AF' setting to 'MF'.
Did you know that you can adjust the viewfinder to your eyesight?
With EOS single-lens reflex cameras it is essential that your eyes can focus on the image displayed in the optical viewfinder. You can wear glasses to help with this, but it is often better to make use of the built-in dioptric correction lens. This is adjusted using the small wheel at the top right of the viewfinder eyepiece. Look into the viewfinder and turn the wheel in one direction and then the other until the black rectangles that indicate the position of the focus points are at their sharpest.
This tutorial gives a good start into understanding the autofocus capabilities of your EOS. If you would like to know more, Canon Professional Network (CPN) offers an in-depth explanation. Read all about AF here.