Task:  have to leave for the cooking class in the next 30 minutes, but before that, I need to complete an important task. Set a timer for 30 minutes in the clock app so that my cooking class  will not be missed.
Steps:
open the Clock app
Click on the Timer section at the bottom of the screen 
Set minutes to 30
Set minutes to 30
Set minutes to 30
Set minutes to 30
Click on the play start button of the screen