How to use stream tags

Hi there,
I have used the gnuradio and usrp to implement a three nodes poll
network and that works perfectly.
Now I want to implement a tdma network.
I notice the stream tag can be used to implement synchronization , but
I don’t know how to use it.
I search the web and found little useful information about how to use
the stream tag(or i just don’t get it).
can anybody show me some material?some code using the stream tag would
be much better.
Appreciate in advance.