One sign-in links the extension to your Artra account. It uses your normal Artra login, nothing LinkedIn-specific.
Click the Artra icon in the Chrome toolbar. The side panel opens on the right of whatever page you are on.
On the "Prospect" tab, click "Sign In" and use your Artra login (Google, Microsoft and SSO work too).
The "Max" tab is Max as a side panel: ask about the page you are on, or add the person you are looking at to Artra.
The gear sets the hours Artra may work in Chrome (weekdays 8 to 6 by default).