Each of your class features is detailed in the remainder of the class description. If a class feature ever requires a calculation or produces a numerical result that would include a fraction, always round down unless otherwise stated. This follows the normal rule for rounding (see page 243).
Class features may reference different types of levels, such as character level, class level, and caster level (if you’re a spellcaster). For a character with only one class, these are all the same thing. If you decide to take multiple classes, when a class feature has an effect or prerequisite based on your level, it always means your level in that class, not your total character level (which is the sum of all your different class levels). If a class feature or spell mentions your caster level, that refers to your combined levels in all spellcasting classes (though the number of spells you can cast per day and the number you know at each level are still based on just the level of the class granting them).
Class features usually fall into one of three categories: extraordinary abilities, spell-like abilities, and supernatural abilities. You may gain these abilities through one or more of a variety of means, including advanced meditative techniques, athletic training, biological stimulants, cutting-edge technological devices, experimental cybernetic enhancements, mysterious alien technology, or state-of-the-art biotech. The specific source of these abilities is up to you, as a way to add flavor to your character. Regardless of the source, these abilities are class features and cannot be taken away from you, though they may be suppressed or negated by other effects (see below).
Extraordinary Abilities (Ex): Extraordinary abilities are nonmagical, despite the fact that they’re not something just anyone can do, or even learn without extensive training. Effects or areas that suppress or negate magic have no effect on extraordinary abilities.
Spell-Like Abilities (Sp): Spell-like abilities are magical abilities similar to spells. Spell-like abilities are subject to spell resistance (see page 265) and do not function in areas where magic is suppressed or negated. Spell-like abilities can be dispelled.
Supernatural Abilities (Su): Supernatural abilities are magical but not spell-like. Supernatural abilities are not subject to spell resistance, but they don’t function in areas where magic is suppressed or negated. A supernatural ability’s effect cannot be dispelled.