Hey, relax! This is so common that I almost laugh over it now. This issue is most probably with the Kura you have installed. It must be without the web ui.
If you check out the official download page again, you'll see in its right column that says Kura 1.3.0 Extended Downloads and here's what its description says:
The below downloads contain the Kura Web UI, [...] These features, while released under Eclipse Public License, depend on third party libraries that cannot be distributed directly by Eclipse.
So, all you'll need to do is go back and download the suitable version this time (and Developer Workspace) from that right column and reinstall this version of Kura with the web ui.
And, if you think your installed version is already the one with the web ui, then you'll have to share your /var/log/kura.log and /var/log/kura-console.log as they really help in finding and resolving such errors.