[R] Newbie trying to understand $ so I can understand acf function in stats

I am trying to understand the function acf stats:::acf shows me the function I am having trouble understanding the usage "$acf" in the following acf <- array(.C(R_acf, as.double(x), as.integer(sampleT), as.integer(nser), as.integer(lag.max), as.integer(type == "correlation"

[R] Newbie - want to view code for a function

Brand new to R Want to understand the algorithm used in yule-walker time series autoregression model I assume there is a way to see the source for ar.yw I also assume that everybody except me knows how Could someone suggest to me how to find out I've looked thru some of the documenttion - th