While it is possible to take a picture of something by pointing your camera in the right general direction and pressing the shutter release, you will likely get a much better image if you pay some attention on focus. And "focus" has more than one meaning.
To begin with, when a lens is focused at some given distance, only objects exactly that distance away will be rendered truly in focus. Objects immediately in front of or behind that distance will appear to be acceptably in focus, the difference being negligible enough that no one would or could notice. The further from that set focus distance an object is though, it will start to appear progressively softer to the point not only will people notice, doing so becomes unavoidable. The range of distances over which an image is acceptably in focus is termed the depth of field (DOF).
I've written extensively on depth of field before, and I'm not going to repeat myself here, but the question I do want to address is: what should you focus on? The obvious answer is that you should focus on the subject of your image, but that requires some thought. Unless you have a very simple image, there will likely be more than one thing in it. They can't all be your subject, or can they? Can a forest be your subject, or do you have to focus on a single tree? The choice is yours, but you can generally create a stronger image that connects more strongly with a viewer by giving them something specific to focus on. Find the one that calls out to you the most and position it in the frame where you want it. Focus on that. This likely won't always be easy, but the more in tune with what your subject is, the better image you are likely to create. Consider it a challenge.
Creative depth of field is an interesting subject. On the one hand there are seemingly infinite landscapes with everything from the closest flower to the furthest mountain in focus. On the other, there are soft, subtle images with only a single blade of grass or flower petal in focus. At least some subjects can successfully be shot both ways, or anywhere in between. What you do is just as much of a choice as is where to focus. The main control for achieving the depth of field you are after is of course the lens aperture but don't forget that your distance from the subject has a bearing as well since it changes the relative spatial relationships between your main subject and everything else in the frame.
Traditionally, the camera's depth of field preview button has been the safest way to tell what will actually appear to be in focus when the shutter is fired, but digital photography presents new possibilities. These days, it is entirely possible to simply guess at depth of field and check things after the fact by zooming in on the LCD screen image. If you didn't get what you were after, make the necessary adjustments and try again.
When taking a photo, "focus" deals with appropriately setting the camera controls to determine what is in focus and what appears to be. When viewing an image, "focus" has more to do with where the eye naturally falls and how it moves around the frame to examine and admire it. There is a relationship between these two meanings for the same word, but they are not necessarily synonymous. Sometimes you can guide a viewer to see what you want them to by ensuring that it is the sharpest thing in the frame. Other times a softer focus can better accentuate the mood you are after. Color, shadow and line can also guide a viewer's focus. It is up to you to decide how to capture what you are going for. Photography is very much about technical things when dealing with shutter speed, aperture and so on, but it is also very much about creativity when dealing with how you employ those technical tools.
Make taking pictures the result of a series of conscious choices, not a haphazard activity. What you focus on and how is a big part of creating great images.