I just got a new lens (Nikon DX 55-300) for my Nikon 3300 camera. I am just a beginner, however when I try to focus and capture something semi- close by (in the same room) it does not allow me to focus or shoot the image. The only way to capture the image is if I flip the manual focus switch on the side. Why is this? Does it have to do with aparture or ISO. Also, I am taking a trip to South Africa and need all the beginner help I can get in order to learn my camera quickly.
This lens is advertised as having a minimum focus distance of 1.4m. That means it can't focus on subjects closer than that distance — about 4.5 feet. That might be some of your problem.
It is also likely that indoors is darker than you think it is — sunlight is many times more light than the typical interior. The lens may have trouble focusing in low-light conditions.
Many cameras have what's called "focus priority" shutter modes, where the camera won't click the frame until it's decided that the subject is in focus — and if it can't get focus, it won't let you take a picture. This is the default on your Nikon D3300. (Of course, disabling that mode doesn't solve the focus problem, but it does explain why you can get pictures in manual mode.)
What other lenses do you have? What subjects do you plan to photograph? If there is a mismatch between your intended subject matter and lens choice, you should consider getting a more suitable lens. Since you "just got" this lens, you may still be within the return window.
As mattdm mentions, the lens is likely unable to focus closely because of its minimum focusing distance. Although you are able to fire the shutter with the lens in manual mode, the images you capture may not be optimal. If there is sufficient light, stopping down the aperture can widen the depth of field and help make closer objects appear more in-focus.
You may be able to switch the camera to "release priority" mode, where the shutter will fire regardless of whether focus has locked. However, this will likely increase the number of out-of-focus shots you will obtain at all distances.
As tetsujin had formerly noted, the lens has a slow F4.5 max aperture. That would make it a good daylight lens with marginal indoor performance (which mattdm also notes). Attempting to adjust the aperture in this case would be unhelpful because the camera likely focuses with the aperture wide open regardless of the setting.
You can try adding more light, as mattdm comments. This could be in the form of a focus-assist or constant light source. A speedlight without focus assist would not be helpful.
A controversial source mentions that the lens' autofocus is slow. The camera may be giving up on attaining focus before the lens is able to complete its focusing routine. Adding a focus assist light may help. Otherwise, there isn't much you can do besides get a different lens or camera body.