There are a lot of things you have to consider with you work with lights in 3D space. When you are having problems a screenshot that does not show all of the properties of all of the layers giving you problems is not much help. It looks like you have set the comp background to grey which does not gain you anything in the final render and may cause problems if you render with alpha channels, and your comp has one light, one layer, the view is set to Custom View 1, the magnification ratio for the Composition panel is 100% and the rendering for the comp panel is set to Full (Auto is the best choice 99.9% of the time), and Fast Previews is NOT set to Draft because the icon is not blue. The custom view you have chosen will not show 2D layers and most importantly, WILL NOT RENDER except for previews is really only useful to line up your set pieces in 3D space. By set pieces I mean the layers, the camera and the lights.
Let's talk briefly about Classic 3D vs real world lighting to start with. In the real world light bounces off everything so a single point source, even like a spot light, will light up other things in the scene. In a 3D environment, unless you turn on ray traced rendering and add a bunch of paths light doesn't bounce off anything. The more paths the longer things take to render.
Now that you understand that basic fact let's talk about the way to overcome that problem. With only one light there is no Ambient light to give some light to anything that does not have light from your spot light directly falling on it there will be no light on anything else in your scene. NONE. The solution is to add an ambient light to the scene to give you some base illumination. Let's also talk about fall off and material options for just a moment. Material options are the editable properties of a 3D layer that control how the light effects that layer. You can reveal Material Options and Light Options by selecting your 3D layers and your lights. You need to play with these properties to figure out what they will do. I have arranged my workspace to show you everything I'm talking about. This is a good way to experiment with lights to figure out how they work:
I would add light types to a simple scene and try and figure out how things work. To learn more about lighting type "lights" in the Search Help field at the top right corner of AE and check out some of the training and help resources that brings up. Adobe - Search: lights