well,
I now can play some tunes, and I would try to enter sessions; but I noticed I never knew the tunes usually played insessions; what would you recommend to learn? What are the “must-know”?
Thanks
That depends hugely on the session. The best thing to do is to pick a session and go to it several times. You’ll be able to find out the tunes they like to play there (ask someone if you don’t hear the name), as well as find out how fast they play them and which tunes they typically put together in sets.
It’s probably always best to get a feel for a session before you show up ready to play. It’ll make it a lot easier for you, and it’ll make the others there a lot happier to welcome you into their midst.
Enjoy! 
Steven
The BBC 2 virtual session site has some of the most commonly played Irish session tunes (Played well and at a reasonable speed, and with sheet music).
I’m not good with computers but I think this is the address - if not use a search engine. Good luck and have fun!!