In the brackets, you list all the output variables that you want your function to return. If it returns only one variable, then you can omit the bracket - they're required for 2 or more returned values.
The parentheses contain the input arguments. You list them separated by commas. For example
function theSum = GetSum(a, b)
theSum = a+b;
or
function [theSum, theProduct] = GetSumAndProduct(a, b)
theSum = a+b;
theProduct = a*b;
