You cannot "Save As" a video file. To create a watchable movie (MP4, MOV), you must it. You add the composition to the Render Queue.
Adobe After Effects CC 2017 remains a powerful tool for beginners and pros alike. By mastering the Timeline, Keyframes, and the new Cinema 4D renderer, you can create professional motion graphics. Remember: After Effects has a steep learning curve, so start by animating simple shapes before moving on to complex visual effects. adobe after effect 2017
To understand After Effects, you must understand these five concepts: You cannot "Save As" a video file