Only a few archetypes, like the Qinggong Monk, allows you to freely pick between the original abilities and the archetype abilities. Others must follow the general rules for archetypes, which replaces or changes all the class abilities listed on the archetype:
The primary way in which archetypes modify their corresponding base classes is via the use of alternate class features. When a character selects a class, he must normally choose to use the standard class features found in the class’s original source—the exception is if he chooses to adopt an archetype. Each alternate class feature presented in an archetype replaces a specific class feature from its parent class. For example, the flowing monk archetype’s redirection class feature replaces the Stunning Fist feature of the standard monk class.
When an archetype includes multiple alternate class features, a character must take them all—often blocking the character from ever gaining certain standard class features, but replacing them with other options. All other class features of the base class that aren’t mentioned among the alternate class features remain unchanged and are acquired normally when the character reaches the appropriate level, unless noted otherwise. A character who takes an alternate class feature does not count as having the class feature that was replaced for the purposes of meeting any requirements or prerequisites.
A character can take more than one archetype and garner additional alternate class features, but none of the alternate class features can replace or alter the same class feature.