In all cases, use the function name followed by a list of expressions, separated by commas, of data type corresponding to the function prototype.
Today() // no parameters
GetEasterFor(nYear) // one parameter
The result of a function call can either be assigned to a variable
nToday = Today()
nDateEaster = GetEasterFor(nYear)
or it can be used as parameter of another function call, as below, in nested function calls.
nWeekDay = WeekdayOf(Today())
nMayFirst = FirstDateOfMonth(YearOf(Today()),5)
Some functions are called void, because they do not return any result. These are usually function that act on the database or on the textbox that contains the current macro token. They are called simply, without assigning their result.
See also: list of all macro functions.