Summarize:

Select the AC or DC voltage mode, depending on the circuit you want to test, which is indicated by a straight line with dots for DC or a wavy line for AC.  Electricians and beginners tend to prefer digital multimeters because they are faster and easier to use. DC and AC are also commonly represented by DCV and ACV, respectively. Find out the regular voltage of the thing you want to measure and set the middle dial one level above that. So, if you want to measure a 120v outlet, set the dial to the AC side at 200v. Choosing a high range prevents damage from having too low a setting for a high voltage.  Damage is uncommon when measuring low voltages, but if you set your multimeter to 20v and try to measure a 220v outlet, you might destroy it and have to replace it entirely. If your analog multimeter is set too high, the needle will barely move. Lower the setting if this is the case to get an accurate reading. If your analog multimeter is set a step too low, the needle will fling to the right. Quickly remove the probes from the connection to sever the circuit and prevent damage to your multimeter if this happens. Hold each probe by the protective plastic coverings and plug them into the corresponding terminals. This is best tested with a battery, if this is your first time using a multimeter, as the positive and negative sides are clearly labeled. It is sometimes recommended to attach the black probe but only touch the red probe to the positive terminal, as if there is an error you can quickly lift the probe and break the circuit. Look at the needle to see if it moves to around the middle of the display. There are various levels of voltages displayed behind the needle, so find the row that corresponds with the range you chose earlier. Take down the measurement, and consider repeating the test a few times to make sure the needle is reading accurately.  Remember to start at a high range and work your way down. If the needle barely moves, select a lower range to get an accurate reading. If the needle flies off to the right, you need to break the circuit and select a higher range. If it flies to the right too hard, it might damage the needle, so try starting at a high range.
Select the AC or DC voltage mode on the multimeter. Choose a high range to start with, then lower it until the needle reads accurately. Attach the black probe to the negative terminal and the red probe to the positive terminal. Check the needle to see if it displays the right voltage, and make adjustments.