First Conditional

• 
• You can also use the first conditional can, must, or an imperative. 

  
  

  If + present simple, can/must + base verb

  -If it rains, you can use an umbrella.

  
  

  If + present simple, imperative

  -If it rains, use an umbrella.

• If there is a fire, you can call the firefighters.	We must take shelter if there is a tornado.*
  If you are tired, take a break.	Eat something if you are hungry. *

• *Remember! You can use the verb before the if clause without a comma.

 Source : Alison