So, I was rotoscoping to make a green screen video, and the rotoscope was working great. Then, I went to the next frame, and the selection wasn't right at all, so I made the brush big to remove all of it. Then I started doing it normally again, but it was like I was just painting on the frame. It didn't select the colors or ANYTHING, just like I was drawing on the frame. I have almost always had this problem, no matter how much I update my software or computer. Please help!
My computer is Windows 10 64-bit and version of After Effects is After Effects CC 2017
Show us screenshots of your timline and layer panel with the Rotobrush mask and the spans visible. I get the feeling that you are simply using the tool wrongly.
This sounds to me like you have not gone through the training materials on RotoBrush. Rotobrush is a type of rotoscoping but it is not intuitive and depending on the shot, it may not work at all. If you have not studied up it's highly unlikely that you are using the tool correctly. Just type rotobrush in the search help field at the top right corner of AE and study up, then if you still can't get the tool to work we need to see what your video looks like or better yet, a screenshot of your project with all modified properties of the layers and the entire Layer panel revealed.