I am trying to write a SOQL query to return the Field Names, API Names for all custom fields in my org.

I have checked the box for Use Tooling API. When I write this: 
Select Description, Field Name, Id, from customfield 

I get this message: 'only aggregate expressions use field aliasing' 
 

Can you please tell me how I can write this SOQL query correctly? 
THanks!