square(x) = x * x
y = square(3+4)
There are many different conventions for passing arguments to functions and procedures including call-by-value, call-by-name, call-by-reference, call-by-need. These affect whether the value of the argument is computed by the caller or the callee (the function) and whether the callee can modify the value of the argument as seen by the caller (if it is a variable).
Arguments to functions are usually, following mathematical notation, written in parentheses after the function name, separated by commas (but see curried function). Arguments to a program are usually given after the command name, separated by spaces, e.g.:
cat myfile yourfile hisfile
Here "cat" is the command and "myfile", "yourfile", and "hisfile" are the arguments.