Three patterns, three different faults
The test pattern has three bands. Across the top are the standard colour bars: white, yellow, cyan, green, magenta, red, blue and black, in the order broadcast engineers have used for decades. In the middle is a 32 step grey ramp. Along the bottom is a smooth black to white gradient. Each band catches something the others do not.
Reading the colour bars
Each bar should be a flat, even block with a hard edge against its neighbours. Look for bars that are not flat, for colour fringing along the vertical edges, which points at sharpening or a scaling problem, and for a brightness difference between the left and right of the same bar, which is a uniformity fault.
Reading the 32 step ramp
You should be able to count distinct steps from black to white, and crucially you should be able to see the difference between the first step and pure black, and between the last step and pure white. If the darkest few steps all look identically black, your black level is crushed and you are losing shadow detail in everything you watch. If the brightest few all look identically white, the whites are clipped. Both are usually fixable in the monitor menu with the brightness and contrast controls, in that order.
Reading the smooth gradient
The bottom band should be a continuous fade with no visible edges. Vertical stripes across it are banding, which means the panel or the signal chain is not carrying enough bit depth. A fine crawling grain is temporal dithering, which is how a cheaper panel fakes the missing bit depth, and it is normal on most consumer displays.
Banding that appears only in a browser or only in one application is often a colour management problem rather than a panel limit. Try the same pattern in a different application before blaming the hardware, and check whether the graphics driver is outputting limited range rather than full range, which crushes both ends and exaggerates every banding artefact.