How to use Multi Select Field in formulas

How to use Multi Select Field in formulas

Hi, 
    In my deals module I have a multi select field called products. It contains Product 1 , Product 2 , Product 3  
I am trying to create a formula field to check if "product 1" is selected . May I know in zoho crm which formula do i use? I have tried Contains function but there is a syntax error.