To view active sessions or end access on other devices, click your profile image in the top right corner (desktop) or bottom right (mobile/app). Select Account Settings → Security → Manage Sessions.

Here you see a list of active sessions with browser, OS, last activity, and IP address. To end a session, click the red cross. To log out of all devices at once, click Log out of all sessions at the top of the page. This is especially useful if you suspect someone else has access or you forgot to log out on a shared device.