1.17: you need acf(). For a histogram you may want to specify larger (then default) number of breaks.
1.18: decompose() can do the job (check ? decompose). However, before you  use it, you should create
a time series object which will have information about your TS frequency in particular: if your data is in x,
then what you need is x_ts=ts(x, freq=...). Save a result of decompose(x_ts)  in, say, dec_x. Then graph
it: plot(dec_x). Try different frequencies... look at the graphs of the trend and seasonal components. What is
the "best" frequency value? Does it coincide with your expectation (recall where this TS came from)?