When drawing plans and sections, it is useful to use different types of line. These can indicate whether an object is above or below another or has a temporary position. In AutoCAD these types of line are called Linetypes and are associated with AutoCAD's Layer system, which allows a user to group similar objects together. All the objects on a Layer would have the same Linetype and colour, making the group easily identifiable.
Open AutoCAD. Type "layer" at the command line, then press enter. This will open the Layer Properties dialogue box.
Click on the layer whose linetype you want to change. Make sure you click on the layer's linetype name. This will open the Select Linetype dialogue.
Click on "Load" to open another dialogue box. This contains all the Linetypes available in AutoCAD. Select the Dashed Linetype you want to use. Click "OK."
Click on the "Dashed Linetype" that has now been loaded into the Select Linetype dialogue. Click "OK" to apply that linetype to the selected layer. When you draw on that layer all lines will now be dashed.
You can load multiple Linetypes by holding down the "Ctrl" key while making your selection. These are all then loaded and available, although only one linetype can be assigned per layer.