Type your message/upload your attachment.
Click on the Read Receipt icon as directed by the arrow as shown in the figure below.
Note: The Step1 and Step2 can be done vice-versa.
Click on Send.
The applied read receipt message is seen in this way as shown in the figure below.
Once the read receipt is acknowledged by the recipient, it turns into a solid blue color by giving an indication to the sender that it was read by him/her. Find it in the figure shown below.