RPM packages installation

Hi, there!
How is the right way to install RPM packages on Leap 42.1 (Plasma 5)?
In Dolphin, when I click on a RPM package, Ark shows the content. It don´t install the package. (I was trying to install Google Chrome.)

Also, cannot select root user at login, in graphical mode.

Thank you, in advance.

You should never do that. There is no need and only danger.
Read this: SDB:Login as root - openSUSE Wiki

You can e.g. use zypper (as root) to install an RPM

zypper in path-to-file.rpm