[R] using arima() function

[Yan Yu]

HI, there, 
     When i use R, i tried to use function arima(), it complains:
Error: couldn't find function "arima"

But when I type "help.search("arima") ",
I got arima() poped up..

arima(ts)               ARIMA Modelling of Time Series
arima.sim(ts)           Simulate from an ARIMA Model
arima0(ts)              ARIMA Modelling of Time Series -- Preliminary
                        Version

Do i need to include some path? 
THANKS a lot for any hints!
yan