A line starting with
function
is the first line of a function definition. That means it must go in an m-file - usually it is the first line in the file. You can't define a function with this syntax on the command-line.
In a function definition, the thing in parentheses () must be the name of a variable (or more generally a comma-separated list of variable names). It can't be a string. When you call a function, you can give a string as an argument - but when calling a function you don't use the function keyword.
