If you were unaware, kerning is the process of adjusting the spacing between two letterforms (oops! not an olympic sport!), whether they are in print, on the web, or any other place. (Tracking, on the other hand, adjusts the space uniformly over a range of letters.) Graphic designers kern text to position it gracefully into the allotted space, making a better design – but just as importantly, kerning can increase readability.
If you’re just learning how kerning works there’s a great website out there: “Kern Type, a kerning game.” In Kern Type you’re presented with a word on the screen, and two or more of the letters are pretty obviously not spaced correctly. You use your arrow keys (if you’re on a PC, or just touch the screen if you’re on a tablet) to move the letters right or left until you think the word is spaced correctly. Press Enter to get your score – and see how close you are to the professionals. (Wait til you get your first 100!) An added bonus is that the words are displayed in a myriad of typefaces – good exposure to how kerning works across different fonts.