Create a new group in the webdock (sidebar), by clicking on the plus icon. You can name a group and give it a color. Then start with an app or just a set of tabs.
Groups are your go-to place for completing everyday tasks, and each one contains its own Wavebox apps and tabs. You could for example create a group for Google, and use it to keep your Gmail, Google Drive, Calendar, and other Google-y stuff; or, you can create a 'News' group with BBC News, CNN, and the other news sites you use daily.
Each Group has a name, icon, and color in the webdock (sidebar), it displays an unread badge propagated from all the apps within it, meaning you stay up to date with everything that's going on in that group.
To customize the Group at any time, right-click on its icon in the webdock, then click on the icon or name to make any changes. For more settings, right-click on the icon and go to Settings > Group Settings.