Yandex.Geocoder
Geocoding is easy.
For forward geocoding you should create GeocodeRequest and execute it.
var request = new GeocoderRequest { Request = "Ярославль серова 13" };
var client = new GeocoderClient();
var response = await client.Geocode(request);
var firstGeoObject = response.GeoObjectCollection.FeatureMember.FirstOrDefault();
var coordinate = firstGeoObject.GeoObject.Point.Pos;
var addressComponents = firstGeoObject.GeoObject.MetaDataProperty.GeocoderMetaData.Address.Components;
var country = addressComponents.FirstOrDefault(c => c.Kind.Equals(AddressComponentKind.Country));
var province = addressComponents.LastOrDefault(c => c.Kind.Equals(AddressComponentKind.Province));
var area = addressComponents.FirstOrDefault(c => c.Kind.Equals(AddressComponentKind.Area));
var city = addressComponents.FirstOrDefault(c => c.Kind.Equals(AddressComponentKind.Locality));
var street = addressComponents.FirstOrDefault(c => c.Kind.Equals(AddressComponentKind.Street));
var house = addressComponents.FirstOrDefault(c => c.Kind.Equals(AddressComponentKind.House));
Assert.Equal("Россия", country.Name);
Assert.Equal("Ярославская область", province.Name);
Assert.Equal("городской округ Ярославль", area.Name);
Assert.Equal("Ярославль", city.Name);
Assert.Equal("улица Серова", street.Name);
Assert.Equal("13", house.Name);
Assert.Equal("39.802311 57.608719", coordinate);
For reverse geocoding you should create ReverseGeocodreRequest.
var request = new ReverseGeocoderRequest { Latitude = 58.046733, Longitude = 38.841715 };
var client = new GeocoderClient();
var response = await client.ReverseGeocode(request);
var firstGeoObject = response.GeoObjectCollection.FeatureMember.FirstOrDefault();
var addressComponents = firstGeoObject.GeoObject.MetaDataProperty.GeocoderMetaData.Address.Components;
var country = addressComponents.FirstOrDefault(c => c.Kind.Equals(AddressComponentKind.Country));
var province = addressComponents.LastOrDefault(c => c.Kind.Equals(AddressComponentKind.Province));
var area = addressComponents.FirstOrDefault(c => c.Kind.Equals(AddressComponentKind.Area));
var city = addressComponents.FirstOrDefault(c => c.Kind.Equals(AddressComponentKind.Locality));
var street = addressComponents.FirstOrDefault(c => c.Kind.Equals(AddressComponentKind.Street));
var house = addressComponents.FirstOrDefault(c => c.Kind.Equals(AddressComponentKind.House));
Assert.Equal("Россия", country.Name);
Assert.Equal("Ярославская область", province.Name);
Assert.Equal("городской округ Рыбинск", area.Name);
Assert.Equal("Рыбинск", city.Name);
Assert.Equal("улица Бородулина", street.Name);
Assert.Equal("23", house.Name);
Also you may use all additional parameters from https://tech.yandex.ru/maps/doc/geocoder/desc/concepts/input_params-docpage/