Learn how to use WhatsApp's pencil tool to draw on pictures and videos before you send them!
Steps

Step 1. Open WhatsApp Messenger
The WhatsApp icon looks like a green box containing a text bubble and a small phone.
If when WhatsApp opens you don't land on the conversations page, tap the Conversations button

Step 2. Choose a conversation
It will open.

Step 3. Tap the camera icon next to the text field
It is located to the right of where you type your message at the bottom of your screen. When you tap it, your camera opens.

Step 4. Press the round button to take a photo
If you prefer to make a video, do a long press on the same button. It is represented by a large white circle and is located at the bottom of your screen.
You can also select an image in your phone's Camera Roll app, from the list above the round button

Step 5. Tap the pencil icon at the top right of your screen
You can use the pencil tool to draw on photos, videos, and images in your Camera Roll, before you send them.

Step 6. Choose a color
Tap the color picker on the right and swipe your finger over the color you want. The pencil icon will tell you what color you are currently using.

Step 7. Place your finger on your screen and drag it
A line will then appear on the screen.
You can go back by tapping on the curved arrow icon, on the toolbar at the top of your screen

Step 8. Draw on your screen
With your finger, draw on your image or video. You can choose different colors for each of the lines you draw.

Step 9. Press the Submit button
It's the little paper airplane at the bottom right of your screen.