The Temporary Bonus Sub-Tab can be used to apply conditional bonuses to your character such as Spell effects, bonuses due to Rage, having a familiar within 5 feet of your character and more. These bonuses are situational and are useful to see how they would effect your characters stats. Rage, for example, has a number of bonuses and penalties associated with it and this provides a convenient way to apply them in one step. You can then output a separate sheet for when you character in enraged.
Some Temporary Bonuses like Rage are only available to those characters who have acquired the ability. There are many Temporary Bonuses which are available to any character when the situation calls for it. There are conditional templates such as Fatigued and Exhausted. Many spell effects are available this way because they can be cast on characters by other characters and thus you would not need to have the spell on your spell list to benefit from it. The craft skill and some others have penalties which can be applied if your character does not have the correct tools for the job.
Apply any Temporary bonuses you want by selecting the bonus and clicking Apply Bonus. Certain Temporary Bonuses have to be applied to weapons or other equipment, when you select that type of bonus a list of qualifying equipment your character possesses will be displayed in the right side pane of the tab.