For many people interested in learning to play the fiddle in a traditional style - be it Irish, Scottish, English, Scandinavian, Breton, bluegrass, klezmer or any other style - what they aspire to is playing with other people in informal groups. And with good reason - group playing is great fun!
These events, where people gather to play tunes together in a relaxed environment are often called 'sessions'.
But before you jump right in and join a session, it's important to understand a little more about how they work, and the etiquette that goes along with playing in one. All sessions have slightly different unwritten rules, but the following will help.
The first to understand is that session playing is not the same as a jam. There is improvisation, but on a micro level - at an important level, the players are all playing the same tune. This means in most sessions, you should only play a tune if you know the tune and can confidently play along with it at the speed it is being played. Anything else will 'muddy' the sound of the session. (There are 'beginner' sessions where you can learn or work out tunes as they are played, but these are slightly different).
So, if you want to join a session, sit and listen for a while first. Do you know any of the tunes? What sort of standard are the other players.