I am trying to create some formulas in opportunities. I want to set up some global variables that will be applied to all opportunities. e.g global variables will set for a minimum margin levels, minimum fees etc and within each specific opportunity a formula will determine if the opportunity meets our business objectives. 

 

Can someone please tell me how I go about setting up global variables (e.g. set up a new custom tab?) and how I reference these variables from within the formula. NB I am a user not a developer, so please don't assume too much prior knowledge !!!