In both the left and upper borders of a document window, you will always see a document ruler which shows the real measurements of your document in the current page measurement unit.
Use the mouse to drag guides from the document rulers and place them in your document, or in the work area. If you place a guide and release the mouse button over the document, the guide will only be drawn in the document. If you release it outside the document, the guide will be drawn in the work area too.
Hint: Basically, you can only drag horizontal guides from the horizontal ruler and vertical guides from the vertical ruler. If you want to drag a vertical guide from the horizontal ruler, keep the [Option] key pressed before you click into the ruler. The same is true for dragging horizontal guides from the vertical ruler.
Hint: If you place guides on master pages and switch their magnetism on, they will only be magnetic on master pages. Similarly, guides on layout pages are only magnetic on layout pages.
