If you plan to copy and paste the graph to another program, or place the graph on a Prism layout, you won't really care where it is on the page. But if you plan to print that page, you might care to position a graph precisely.
To see the position of a graph on the page: Drop the View menu, choose Zoom, and choose To Fit Page. This lets you see the entire page at once, so you can see the position of the graph relative to the entire page.
To center the graph on the page: Click on the Center on page button in the Arrange section of the Prism toolbar.
To drag a graph on the page: Grab either axis and drag the graph.
To specify an exact position on the page: Click on the Format Axis tool in the Prism toolbar and enter the exact distance of the graph from the top and left edge of the page in the Frame and Origin tab of the Format Axes dialog.