I want to make blank postcards - 4 to a sheet

hey

Text boxes could be easier to get to the correct size and move around your document. You need to have the drawing toolbar shown - right-click anywhere on the main toolbar area and left-click on Drawing - it should now be shown on the bottom area of your document with a number of small icons. You may well need to experiment to get exactly what you want. From what you have said I think you would need to use the rectangle tool to get the size that you need. Left click on Rectangle, move your mouse pointer onto your document and then drag out a shape. Don't worry if it's not exactly the right size. Whilst the resize handles are shown on it, you can either manually adjust the size or go to Format, Auto shape and type in the exact size that you need.
Additionally, you may need to use the Line tool. Follow the same method as above, but before dragging across the document, hold down the Shift key. This will ensure that the line stays straight even if your hand moves a bit, otherwise you may end up with a lightning bolt line! Make this the size and position that you want, then simply copy and paste the line as often as needed.

Finish off with a text box positioned where you need it inside the rectangle.

Now, use the select objects arrow on the left of the Drawing toolbar. Hold down the Shift key and click on each of the objects you have drawn. Now click on the drop-down arrow alongside Draw and choose Group. All objects are now one item which can be copied and pasted as required.