It is a good idea to go along to your pool and watch a class first to get an idea of what's involved. Make sure the teacher's instructions are clear and that the class isn't over-crowded with no more than 10 learners at a time. Beginners' lessons are usually held in a roped-off area of the shallow end of the pool. Lessons will include how to get safely in and out of the water and then how to glide from the pool edge with floats. Only when you have mastered the arm and leg movements do you begin to learn the proper strokes.
Classes usually last one hour with some including a free practice session afterwards.
Alternatively, ask the leisure department of your local council.