Lucyk--as a "first-timer", I'd suggest you go along as an observer first night---if you enjoy what you see/hear you will be back. If you find the material on show to be familiar and within your repertoire or abilities, then by all means take an instrument along. In a good folk-club environment, you will be given a hearing, and no matter what the level of your competence, your contribution will be respected. And if you are judged well worth listeng to, please don't hesitate to take your gear along to either Guest night or singers night. Guests don't normally perform all through the programme!