Hadoop is all about processing the large data and producing the important statistics with mapreduce programs. In your case you can use the mapreduce programs to analyse your logs to see that which of your online products are viewed most stuffs like that
Q) Is Hadoop only about MapReduce?
A) No it is about larger data processing.
if I can use hadoop for logging or tracking of activities,
you can't use hadoop for server logging it is the task of your app server.
then what is the Map and what would be the Reduce functions?
Map and Reduce are the patterns followed by Hadoop to process the data