It sounds like you are new to After Effects and you have not taken the time to learn anything about rendering and video formats. If you use the Render Cue and the default Output Module settings you get a Lossless file, which is great for further work in the production pipeline but is not intended for distribution or playback. For delivery formats you should be using the Adobe Media Encoder to render an h.264 mp4 file because that is the current standard for distribution. There are many presets to choose from. Whether you use the Render Cue or the Adobe Media encoder, until you have a good understanding of formats and video standards you should not be setting up any custom render settings. The same thing goes for your compositions. Generally they should be HDTV 1920 X 1080 @ 29.97 fps unless you live in a PAL country. If you do you should be picking 25 fps. Monkeying win any other frame rates requires that you have some knowledge of frame rates, their limitations, and that you choose wisely or you'll foul things up.
Please start here: Basic AE
The first lesson was a section on exporting your video. Devote some time to learning about video and don't trust Youtube tutorials from amateurs because more often than not they will start you down and inefficient path that leads to a dead end workflow.
One of the most powerful tools you have is the Search Help field at the top right corner of After Effects. If you want to learn about rendering just type rendering in the search field. If you want to learn how to to motion tracking then type motion tracking in the search field. I've been using AE for more years than Adobe has been developing it and I use search help about once a week for something to make sure that I'm getting the latest good info.