[Ryan F]

Yup, Daniel has the right of it here.

Just in case anyone here now or those who might find this later with a similar question I figure I might as well chip in a slightly more in-depth answer.

Archetypes for PF2 come in a few different varieties currently and they are handled in one of two ways and can be accessed via different areas.

The VAST majority of all Archetypes are added to a Character by way of investing Class Feats that you add just like you would for any other Feat you get for your Class in the main named Class Tab (Ex. The Rogue Tab if you are playing a Rogue) under the Classes subsection you can find in the Navigate Character sidebar. There are OTHER ways to get Archetypes added to a PC in the same named Class Tab such as for an Eldritch Trickster Rogue which gives a special field for the eligible Archetype Dedication or in the case of the Free Archetype Optional Rule you will see a new dedicated option Table that is thusly named where you choose how to spend those specific resources.

For Class Archetypes though, that is handled in a separate Table found typically at the very top of the named Class Tab. At this phase, Paizo has published only a handful of such Archetypes and they instead work by investing Class Feats for them the way it works as Daniel mentioned, is by way of "trading out" certain Class Abilities (or altering the way they work by default) in exchange for the Class Archetype features.

I hope this helps clear up any possible confusion, but if you still do have questions please always feel free to send an email to the support inbox you can find the address for in my signature and we'd be happy to help out.

Thanks!