On the Conditions tab supply the following to condition based off a checkbox field being checked or not.
First condition: This condition
Date A, Field A or Value A: Following CB field
CB Field A: Your checkbox field
Date B, Field B or Value B: Constant Value or String (CB substitutions can be used)
Value B: 1
Condition 1 (> for Dates): A = B (Value A is equal to Value
If it's a multi-checkbox then simply supply the value of that multi-checkbox you want to match for Value B then set the condition to be "does contains".