Click the small star-icons to bookmark/remove bookmarks. Click Add/Remove Boookmark in solarsystem-menu to do the same.

Bookmark pane

Click star-icon in menu to open bookmarks. Click the bookmark to open the solarsystem-menu on that system. Click J-icon to enable/disable that system in DST tab of solarsystem info.

You can drag&drop bookmarks to change their order (browser only).

If cloud is enabled bookmarks get backed up and synced to other devices. They do not get shared.