Setting the kerning, or defining the kerning values, is about adjusting the distance between pairs of glyphs if the space between them looks too loose, too tight, or if some parts overlap with each other with their default spacing.

Once a kerning value has been set for a pair of glyphs, those values can be repeated on every other pair with identical or similar shapes (e.g., V + A, W + A).
Kerning can be set even with already published fonts in most applications (useful in justified texts), but great typefaces usually have these already fixed.