The People tab of the organization page lists all of your colleagues in the organization. This allows you to browse for people to follow. You can also search for people in the organization using the search bar at the top right of this tab.
You can also find people to follow, including those not in your organization, from the People tab of the Browse page. By default, this tab displays members of your organization, but you can switch to the External Catalog to see other users (if your organization allows access to the External Catalog).
To follow a user, click the Follow button.