I guess that the 'check your meter' comment refers to finding out how your meter sets the exposure. You don't need an 18% grey card. Any evenly-lit, evenly-toned surface will do. There are a few ways of doing it. Here's one suggestion. Use aperture priority, and adjust the aperture and lighting so that at your base ISO (100?) you have a shutter speed that is between about 1/8 to 1/30 second. (You can do this exercise for each ISO setting)
Now take a picture at the shutter speed set by the camera (with the evenly-lit surface filing the frame entirely - use a lens hood and avoid flare-causing light sources), and note the shutter speed. Switch to manual and take a series of exposures by varying the shutter speed, not the aperture. The shutter speed variation is likely to be more precise than the aperture variation, so keep the aperture constant. You can vary the shutter speed in as small a step as you can be bothered with, but I tend to go the first two stops in full stops, then go in third-stops.
You now have a set of exposures that tell you roughly how your meter is calibrated and how many stops of range you have under and over that. You find this out by looking at the images in the way you normally do - whether you use JPEG or Raw. In JPEG the auto exposure should have an RGB value of about 119 to 121.
Looking at how your meter/camera behaves in this way may not give you instant answers, but can be a part of an understanding of the behaviour of your camera in terms of exposure.
Good luck,
Helen