[Users] General for openser-2 things

Hello, I'm trying to redirect a call from openser to an Asterisk extension when a call is no answer. I think that this wouldn't be so difficult but I can't do it. I know that I have to use the failure_route(); with a fr_inv_timer parameter and then do a rewritehostport and a rewriteuser. My problem is that when the fr_inv_timer pass the call is cancelled and nothing else happens. In addition, I don't know where I can find the logs that I put in my openser.cfg, I have read the xlog module but I can't understand how to do it. On other hand, I have seen that there are a lot of functions that are often used but I don't know what they do internally, for example t_relay(), t_onreply(), revert_uri(),t_was_cancelled() etc etc etc and I don't know how to use it. ¿Is there any document that explain all it WELL?? Also, I've checked that if I do a call and I put the lines t_relay() and exit that call works fine but if I erase one of the two lines it don't work. Why??? Please help, I want to do a lot of things with openser but there is nothing that explain the basic functionality to do interessant things... Thanks in advance, "It will arrive the day that we will control telephony"