I have been looking through http://docs.basho.com/riak/latest/ but I can't find any doc about the counters.
Basho Hacker Sam Elliott started a CRDT cookbook that will walk you through using the counters in 1.4 (and eventually the new data types we add). That should get you started.
https://github.com/lenary/riak_crdt_cookbook/tree/counter_ex...
Enjoy. Also, come to ricon.io/west.html. We'll be talking plenty about Counters and all the huge stuff coming to Riak in the near future...