Please help, how to add other social networks?

Create a new plugin, add a socialloginproviders folder to it, copy one of my providers into your new folder, update as necessary.

In your Plugin.php add

    function register_flynsarmy_sociallogin_providers()
    {
        return [
            '\\Your\\Plugin\\SocialLoginProviders\\YourProvider' => [
                'label' => 'Your Provider',
                'alias' => 'YourProvider',
                'description' => 'Log in with Your Provider'
            ],
        ];
    }

I don't have time to support free plugins, so you'll have to figure out the rest yourself - but it shouldn't be too complicated. My plugin pulls in HybridAuth so check the docs there for more info.

Your best bet is to copy the Facebook social login provider and use that as a template.