The function head is only defined for an input that is a table, a timetable, or a tall array.
When trying to execute your code, MATLAB sees that there is a method available called head, but that it is not defined for the argument you called it with. The error message is trying to suggest, then, that your input argument is the incorrect type, or that you have perhaps omitted an input argument that is the correct type, such as a table.
If you want to see just the first few elements of an ordinary vector, like your variable x, then index into it like this:
x = 1:100;
x(1:10)
