This is the means to learn new spells or pay a teacher mob to increase your skill proficiency
Practice is a method of scribing your spells. This is done with the help of a teacher in the room. For this to be done, you must have a spellbook and quill in hand and resting comfortably. You can then "practice <spell>" to add a spell to your spellbook. If this command is typed without any parameters and you are in the presence of a teacher it will show your list of spells.
practice (to see a list of spells that may be scribed)
practice <spell> (while holding both a spellbook and quill and resting)
practice all (this will scribe all spells into the book currently held by the player if there is enough room left)
Practicing skills can be done by either two options. The first is passively "notching" skills by using them in or out of battle. For instance a rogue may wish to practice 'hide' by attempting to hide over and over. A second way to "notch" skills is by finding the teacher mobs on the continent maps or in a Hometown, and practicing skills at them by spending money.
practice (to see the cost of practicing particular skills)
practice <skill> (to practice the skill up one level)
Note: Skills will notch automatically to 40 as you gain levels.