Focus is adjusting the camera’s lens to focus on what is important in the scene. Most lenses will have a focus ring that rotates and changes the focus from what is near to what is further away. Most cameras or lenses will have an option for manual and auto focus. Auto focus works relatively good on most cameras and most lenses and is one of the auto settings that is usually recommend using, especially when traveling, doing event photography or even just snapping photos of kids. Auto focus will help take sharper photos more quickly than doing it manually for most beginners.
Manual focus is great when you have more time to set up your shoot and you’re more particular about what specific part of your frame is in focus, to make sure the focus is where you want it to be. Sometimes, if you are in a darker environment, your camera’s auto focus won’t work as well so this would be a case for using manual focus.
When photographing people, you want to focus on their eyes. When doing this remember that aperture affects your depth of field as well, with a wide-open aperture, you can be photographing a person and have their eyes in focus while their nose and ears are out of focus. Doing the opposite and having their nose or their ears in focus, and their eyes blurry, would look off to the viewer, so always try to get sharp focus on their eyes. If your photos aren’t sharp or aren’t focus on what you want them to be focused on, try increasing your f-stop to get a deeper depth of field. It is also good when shooting landscapes where you will probably want to use a larger f-stop, so more is in focus.