If your irssi crashes, it's always a bug. Please read bugreporting howto and send one. For other type of bugs, it would still be nice to hear of them, but chances are that it's already known. You could check the TODO file which comes with irssi if it's already there. Send all bugreports to irssi's bug reporting system.
Read the INSTALL file that comes with irssi, it explains the most common problems.
Read FAQ before asking anything.
Startup-HOWTO is quite
useful as well. And if you just want to know about some setting, you could
very well guess it yourself too, like if you want to change something related
to windows, try