Example:
myX = randi(9, 17, 3);
myY = randi(9, 5, 3) - 5;
myD = pdist2(myX, myY, 'sqeuclidean');
That is, you need to have data to pass into the function. The variable names do not need to be X, Y and metric: you can use whatever variable names are appropriate for your purposes.