public FeatureClassToken Create( 
   FeatureDatasetDescription featureDatasetDescription,
   FeatureClassDescription featureClassDescription
)

public void CreateFeatureDatasetWithFeatureClassSnippet(Geodatabase geodatabase)
{
    // Creating a FeatureDataset named as 'Parcel_Information' and a FeatureClass with name 'Parcels' in one operation

    string featureDatasetName = "Parcel_Information";
    string featureClassName = "Parcels";

    SchemaBuilder schemaBuilder = new SchemaBuilder(geodatabase);

    // Create a FeatureDataset token
    FeatureDatasetDescription featureDatasetDescription = new FeatureDatasetDescription(featureDatasetName, SpatialReferences.WGS84);
    FeatureDatasetToken featureDatasetToken = schemaBuilder.Create(featureDatasetDescription);

    // Create a FeatureClass description
    FeatureClassDescription featureClassDescription = new FeatureClassDescription(featureClassName,
      new List<FieldDescription>()
      {
  new FieldDescription("Id", FieldType.Integer),
  new FieldDescription("Address", FieldType.String)
      },
      new ShapeDescription(GeometryType.Point, SpatialReferences.WGS84));

    // Create a FeatureClass inside a FeatureDataset
    FeatureClassToken featureClassToken = schemaBuilder.Create(new FeatureDatasetDescription(featureDatasetToken), featureClassDescription);

    // Build status
    bool buildStatus = schemaBuilder.Build();

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

public void CreateFeatureClassInsideFeatureDatasetSnippet(Geodatabase geodatabase)
{
    // Creating a FeatureClass named as 'Tax_Jurisdiction' in existing FeatureDataset with name 'Parcels_Information'
    string featureDatasetName = "Parcels_Information";
    string featureClassName = "Tax_Jurisdiction";

    // Create a FeatureClass description
    FeatureClassDescription featureClassDescription = new FeatureClassDescription(featureClassName,
      new List<FieldDescription>()
      {
  new FieldDescription("Tax_Id", FieldType.Integer),
  new FieldDescription("Address", FieldType.String)
      },
      new ShapeDescription(GeometryType.Point, SpatialReferences.WGS84));

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

    SchemaBuilder schemaBuilder = new SchemaBuilder(geodatabase);

    // Create a FeatureClass inside a FeatureDataset using a FeatureDatasetDefinition
    schemaBuilder.Create(new FeatureDatasetDescription(featureDatasetDefinition), featureClassDescription);

    // Build status
    bool buildStatus = schemaBuilder.Build();

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