This is your service discovery panel, which breaks down by component in the sidebar. Each component name and its associated JID is listed to help you find what you need. Most components give you an option to Execute commands with a few exceptions allowing browsing and the ability to join a MUC.

Browse allows you to dig deeper into certain components; for example list the chatrooms available in the MUC component. At the top of the page the specific JID of the component are you in will be displayed. This is a text field, and can be edited to reflect the JID of the component (or just the server name) to navigate.

WebUI Browse Comp

Join to Room will join you to a MUC room that is selected. Alternatively, selecting Join to Room while MUC component is selected, you can join and start a new MUC room.

Execute Command Provides a hierarchy of commands and options to view and edit settings, run commands and scripts, view contents of files, and see statistics. Since each Component can have a unique structure it is best to explore each to see what options are available.