Here’s a review of your focusing options available for viewfinder photography with your Nikon D3300; following that, you can get help with focusing during Live View photography and movie recording.
To many people, the word focus has just one interpretation when applied to a photograph: Either the subject is in focus or it’s blurry. But an artful photographer knows that there’s more to focus than simply getting a sharp image of a subject. You also need to consider depth of field, or the distance over which other objects in the scene appear sharply focused.
A word of warning: The two systems are quite different, and mastering them takes time. You can also learn how to take a picture in the Auto exposure mode, using the default autofocus settings. Then return another day to study the focusing options discussed here.
Thankfully, the concepts related to depth of field apply whether you’re using the viewfinder, taking advantage of Live View photography, or shooting movies.
Regardless of whether you're using the viewfinder or Live View, your first focus task is to set the lens to auto or manual focusing (assuming that your lens supports autofocusing with the D3300). On most lenses, including the D3300 kit lens, you find a switch with two settings: A (or AF) for autofocusing and M (or MF) for Manual focusing, as shown in the figure.
Some lenses, though, sport a switch with a dual setting, AF/M, which enables you to use autofocusing initially but then fine-tune focusing by turning the lens focusing ring. (On this type of lens, you select the M or MF setting for manual-only focusing.) The position of the focusing ring varies from lens to lens; on the kit lens, it’s located in the spot labeled in the figure.