See the following help files:
predict.marssMLE Predict and forecast.
forecast.marssMLE Forecast. Use predict.marssMLE to call with argument h.
plot.marssPredict Plot a prediction or forecast.
autoplot.marssPredict Plot a prediction or forecast using ggplot2 package.
print.marssPredict Print prediction or forecast. If h!=0, i.e. forecast, only the forecast is printed but the marssPredict object (in pred) has all the historical time steps also.