The easiest way I can think of is in this example, suppose you want to check if the bridge on your guitar is correctly earthed, what you would do is set your multimeter to a low-ohms range, say 200 Ohms, you would then touch one of the probe tips to the bridge, and the other to a convenient ground-point, like the sleeve contact of the output-jack, if you got a reading of 0.02 then that would indicate that there was continuity between the bridge and ground, a reading like OL would indicate no continuity, or high-resistance greater than 200 Ohms.