public void AddFeatureClass( 
   FeatureDatasetDescription featureDatasetDescription,
   FeatureClassDescription featureClassDescription
)

// Adding a FeatureClass with name 'Tax_Jurisdiction' into a FeatureDataset named as 'Parcels_Information'

string featureDatasetName = "Parcels_Information";
string featureClassNameToAdd = "Tax_Jurisdiction";

FeatureDatasetDefinition featureDatasetDefinition = geodatabase.GetDefinition<FeatureDatasetDefinition>(featureDatasetName);
FeatureDatasetDescription featureDatasetDescription = new FeatureDatasetDescription(featureDatasetDefinition);

FeatureClassDefinition featureClassDefinition = geodatabase.GetDefinition<FeatureClassDefinition>(featureClassNameToAdd);
FeatureClassDescription featureClassDescription = new FeatureClassDescription(featureClassDefinition);

SchemaBuilder schemaBuilder = new SchemaBuilder(geodatabase);

// Add the 'Tax_Jurisdiction' FeatureClass to the 'Parcels_Information' FeatureDataset 
schemaBuilder.AddFeatureClass(featureDatasetDescription, featureClassDescription);
bool addStatus = schemaBuilder.Build();

if (!addStatus)
{
  IReadOnlyList<string> errors = schemaBuilder.ErrorMessages;
}