An oscilloscope multimeter can measure the voltage of a signal by plotting its graph on a screen. It can also make timing measurements (such as pulse width and frequency) of the signal. It can show how a signal varies over time and help diagnose problems in circuits.
There are many different kinds of signals and thus many different ways to use an oscilloscope. The first step is to choose the appropriate probe for your signal. The simple passive attenuated probe that comes with the scope is fine for most purposes, but there are also active probes available which can amplify the signal and pre-process it before reaching the scope. There are also special probes for measuring current.
Combining Functions: The Power of Oscilloscope Multimeters
Once you have the probe connected to the scope you need to set its vertical position control so that the trace lines up with your signal. Then you can apply the signal and an image should appear on the screen. The other controls are used to select what part of the signal to look at and which channel to trigger on. For example, a pulse trigger can be set to catch a specific part of the signal (such as a rising or falling edge). A slope trigger can be used to find how quickly the signal changes over a certain amount of time.
Finally, there is often a hold-off function to prevent the scope from triggering too soon after its last scan. There may also be a button which lets you find the location of your signal on the screen (beam finder). There are many other functions that an oscilloscope can perform but these are the basics.