If this is the first time for you, come along at least 15 minutes beforehand to the beginners session and ask for one of the coaches. There is ample parking space and kayaks will be available for you to use if you don't have your own.
You will need to have suitable clothing to get wet in and then afterward to change in to. In the winter this is good polypro, jacket and good leg cover, hat/beanie or heavier duty clothes as you see fit. In the Summer ensure you have polypro and leg cover as minimums.
Not every paddler on any one day is at the same level and the likelihood is that you will be placed into a group depending on your ability. If you have not paddled before or not paddled much this may see you on land or standing in water practicing technique for a short period, it may pay to have some feet cover for this.