Hi Olivia,
The best way to start to learn BSL is to learn the Alphabet (finger spell). Once you mastered that move onto the simple signs, hello, goodbye, how are you etc.. Just pick it up from there. There is lots of free videos on YouTube to help you along too. Although please do remember that each part of the United Kingdom may or may not have a different sign from somewhere 20 miles down the road, it's just like us having 'dialect' in English. If you need any help in getting started, don't hesitate to ask
Chrisy