Tap on the camera icon in your Android phone. You can probably see its icon on one of the home screens but in case you cannot, do not panic. The camera app is located in the app drawer which you can access using the main menu button.
When you open the camera app, you will see a viewfinder and a host of options on either side of the screen. In the right corner, if you are holding your phone vertically, you will see a slider button with camera and video camera icons on its two sides. Move that slider button towards the left to switch to the video camera app.
Once you are in the video app, you will see a red recording button. Press that to begin recording.
The length of the video recording depends on the size of the memory card you have. When you think you have recorded enough, press the same button again to stop the video.
You have now successfully recorded a video with your Android phone. Go to your Gallery where you will find the video under the Videos folder to play it.