A formula is a set of requirements that must be met before someone can challenge you to a game or accept your offer for a game in the seek graph.
To set your formula, click on the Settings icon in the main toolbar:
Then choose the 'Formula' tab from the list.
If you want your formula to be used to screen people who accept your seek ad, you must check 'use formula in seek'
Formulas do not apply to "rematch" challenges, and the pools like 1-minute, 5-minute, etc.
For operators and terms for formula, please read "help formula"