To generate output, you can either render your compositions using the After Effects render queue or add your compositions to the Adobe Media Encoder queue with the render settings that you have chosen in the Render Queue panel.

If you don't have Adobe Media Encoder, you need to download Quicktime Software that can get the output Video in mp4 H.264. If you do not download it will not show up in you video option. So Download the latest one that I give the link below.