Hi all - forgive the "noob" question

I have a picklist on my Contracts object, and the possible values are: 'contract type a', 'contract type b, 'contract type n', etc....  I want to setup a formula field where, If 'contract type a' is selected, then the value of the formula field is "x".  If 'contract type b' is selected, then the value should be 'y', so on and so forth.  If no value is selected, it should be '0'.  

I can get one If else to work, but am having trouble adding in the other conditions.  Any help is much appreciated!