About functions
A function is a predefined, named formula that performs a specific calculation and returns a single, specific value.
Most functions include three basic parts:
Each function returns a result of field type text, number, date, time, timestamp, or container.
Function parameters can be constants (such as 1.07 or “hello”), field references (such as InvoiceTotal), expressions (such as 1 + 12), or other functions (such as the NPV function). You can use spaces before or after the parentheses used to enclose the parameters, but spaces are not necessary. When a function requires more than one parameter, separate individual parameters with a list separator, such as a semicolon.
Important  See Design functions for information about literal text parameters.
Curly braces ({ }) surround optional parameters (for example, the Case function and Choose function). An ellipsis (...) signifies that you can add more parameters, each separated by a semicolon (for example, in aggregate functions). Double quotation marks (“ ”) indicate a text string.
This table shows examples of some FileMaker Pro functions.
4, the number of characters in the text “John”
A number representing the starting position of one text string within another, in this case indicating the position of the first occurrence of “Mc” in the Name field
See About formulas for information about where functions can be used.
Related topics 
Functions reference (alphabetical list)
Aggregate functions
Date functions
Design functions
External functions
Financial functions
Get functions
Logical functions
Number functions
Repeating functions
Summary functions
Text functions
Text formatting functions
Time functions
Timestamp functions
Trigonometric functions