JMeter Functions

1. Referenced as ${__functionName(properties)}
    - Like variables, can use in JMeter properties
2. Use Options > Function Helper Dialog
    - Choose a function
    - Enter parameter values
    - Click "Generate", then copy/paste function
3. Helpful functions
    - ${__javaScript(expression to evaluate)}
    - ${__threadNum()}
    - ${__Random(min, max, varname)}
    -  ${__regexFunction(regEx, template, match, ...)}

Was taken from here