When used with an argument, it will practice that particular skill, raising it by an amount dependent on various stats.
In Game Description
Syntax: practice practice <skill> Without an argument, practice will display all skills you currently know and your degree of knowledge of those skills, or what skills are available to you if you are in a guild. If a skill is specified, you will practice that skill provided that you have the practices available and you are in a guild that teaches that skill. Example: > practice > practice backstab SEE ALSO: <Individual skills>, Levels