Hi, Silverstripe depends on mysql db. So, if you have not configured the mysql db or have not provided the right credentials in webpi database form (Step2 of installation), the installation will fail with this error.
Could you attach the webpi log file. That would help us find out what the issue is. The logs are in %USERPROFILE%\AppData\Local\Microsoft\Web Platform Installer\logs\webpi\ and the %USERPROFILE%\AppData\Local\Microsoft\Web Platform Installer\logs\install\ folders. Look for the latest or the log which corresponds to your install