Pearling is generally used for aquarists to determine when their plants are happy and healthy. Plants photosynthesize using water, carbon dioxide and light to create food for themselves and oxygen. When plants in our aquarium build up a bunch of this oxygen they under go pearling. This oxygen is a sign that the plant has also been creating a lot of food for itself to grow. There are 2 different kinds of pearling; one good and the other can be bad.
Above is what good pearling looks like on my Rotala macrandra mini butterfly. Bubbles are collected around the outside edges of plant leaves. This pearling is due to the plant photosynthesizing a lot which in turn leads to healthy fast growth. Pearling like this is a sign of thriving plants. You may see bubbles like this form after a water change which is likely caused by excess oxygen in the water. it isn't coming from the plants like normal pearling so it doesn't necessarily correlate to healthy plant growth.
Not all pearling is good though. A common misconception is that a strings of bubbles being produced by your plants is a sign of good health as well.
In the shot above you can see a couple long strings of bubbles coming from this Bucephalandra. This is due to little tiny holes within the plant leaves due to some kinds of deficiencies in nutrients or the early signs of bad plant health. I have experienced this a lot in crytpocorynes when I make a change in the tank they do not agree with. Pearling like this starts a couple days after the change then old leaves start melting shortly after. This can be fixed by dialing in the fertilization routine for your tank but light and CO2 also play a large factor. This kind of pearling can also be seen when trimming plants and this isn't something to worry about.
How do you get the good kind of pearling? All plants will be slightly different as to when they decide to pearl. Some plants are easier for example Rotala seems to pearl relatively easily compared to most other plants. Well distributed CO2 and strong light will make it easy to achieve pearling for most plants.