Step by step adding Google Font

I’ve reviewed several previous posts about how to add Google Fonts and they are all lacking a major step. The example that referred to has fonts and css already entered. Where do I find this information to replace within google fonts? The documentation does not explain this.

$fonts['PT Sans Narrow'] = 'PT Sans Narrow:400,700';
$fonts['PT Sans'] = 'PT Sans:400,700,400italic,700italic';

The only information I can find for the Google font is:

<link href="https://fonts.googleapis.com/css?family=Metal+Mania" rel="stylesheet">
font-family: 'Metal Mania', cursive;

So I would expect my code to look like:

add_filter( 'avf_google_heading_font', 'avia_add_heading_font');
function avia_add_heading_font($fonts)
{
$fonts['Metal Mania'] = 'Metal Mania:400';
return $fonts;
}
add_filter( 'avf_google_content_font', 'avia_add_content_font');
function avia_add_content_font($fonts)
{
$fonts['Metal Mania'] = 'Metal Mania:400';
return $fonts;
}

This didn’t work so I’ve tried all of the different permutations of 400 and cursive like:
$fonts['Metal Mania'] = 'Metal Mania:400';
$fonts['Metal Mania'] = 'Metal Mania:400cursive';
$fonts['Metal Mania'] = 'Metal Mania:cursive';

So what exactly needs to be replaced and are any other steps involved? We I need to upload the font to the server? Does anything else need to happen in order to change a font?