Logical operators
Logical operators can build compound conditions into a formula, such as two or more conditions that must be met before you choose a particular method of calculation. With logical operators, you can describe such combinations of conditions.
Use AND, OR, or XOR with two expressions; use NOT with one expression.
 
Examples
Use ApplicationReceived="Y" AND FeePaid>0 if you want something to occur only if you have received both the application AND the fee.
Use CurrentBalance0 OR CreditApproved="Y" if you want something to occur only if no money is owed, OR credit has been approved, OR both are true.
Use FeePaid>0 XOR FreeGift="Y" if you want something to occur only if EITHER a fee has been paid or a free gift has been sent, but not both (for example, if a fee has not been paid and a free gift has been sent).
Use NOT IsEmpty(FieldName) to identify records that have a value in the FieldName field.
Related topics 
About formulas