Here we are going to write about how to get system configuration value in your custom file or anywhere else.

Inside the header data file we have add this code

create Data.php file in Magemonkeys/General/Helper/

public function __construct(
   MagentoFrameworkAppConfigScopeConfigInterface $scopeConfig
)
{
   $this->_scopeConfig = $scopeConfig;
}

public function getConfig($config_path)
{
    return $this->_scopeConfig->getValue(
            $config_path,
            MagentoStoreModelScopeInterface::SCOPE_STORE
            );
}

In phtml file – add below for call helper function

$systemconfval = $this->helper('MagemonkeysGeneralHelperData')->getConfig('sectionid/groupid/fieldid');
echo $systemconfval;

Well, after performing above changes, value will be shown. Hope that helps!