Map<String, Country_Codes__mdt> mapCountryCodes = Country_Codes__mdt.getAll();

for(String country: mapCountryCodes.keySet()){

    System.debug(country+' --> '+mapCountryCodes.get(country).Country_Code__c);

}

​

Country_Codes__mdt countryCode = Country_Codes__mdt.getInstance('India');

System.debug('Country Code is--> '+countryCode.Country_Code__c);

​

​