Installing Drupal

According to the documentation I must create a settings.php file and add some stuff to the end. But whenever I create my own settings.php file, installation fails with:

The specified database connection is not defined: default

Anyone ever get it to work?

Friends,

I am trying to download or install a theme in my drupal dashboard. but I cannot find download link. anyone please advise me to install this theme.

theme Link - https://www.drupal.org/project/matrimonial

thank you

I first started with the 8.0.5.zip but there is no install.php
so I reverted back to 7.4.3 installed that version no problem copied the relative files over from 8.0.5 cp -fr drupal-8.0.5/* .
now i see an update.php
but I get this error

I recently had to delete and reupload my drupal 8 site and now it does not appear to work despite the fact that I downloaded a full backup of the site then reuploaded every file exactly the way it was. This message now appear when I visit the site:

I'm in the proccess of installing Drupal 8 for this first time. I have everything setup except the settings.php file.

I've copied the default.settings.php and then go to run the install script. However, I keep getting the error:

Catchable fatal error: Argument 3 passed to Drupal\Core\Database\Database::addConnectionInfo() must be of the type array, string given, called in /core/lib/Drupal/Core/Database/Database.php on line 295 and defined in /core/lib/Drupal/Core/Database/Database.php on line 256

I'm helping my friend to restore the site after the hack that messed a lot.
I have database and all the files but if I replace on fresh install
database then content shows but admin page says error 403 and
main page is asking for user/password. If files are overwritten then

Fatal error: Call to undefined function menu_execute_active_handler() in index.php on line 21

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I just want to restore content and graphics, all the modules/themes/users I can configure once again if admin page is accessible.