Transactional Analysis or TA is a great way of understanding yourself and how you relate to the rest of the world. It uses simple concepts to help you understand your personality. People use it in many ways, eg to work out why they keep getting into difficult relationships, or why relationships keep stalling. They find interpersonal issue that previously seemed unchangeable can become freer, less scary or less upsetting. Some people use it in work or schools, or even to change an entire organisation. It can go deep into childhood or you can stay in the here and now to analyse your own behaviour, thoughts and feelings.
My training was based in this model of understanding personality and human relationships developed by Eric Berne. Whilst I have added other models and approaches to my work, I still enjoy the simplicity and thoroughness of TA. There are 3 youtube videos by Theramin Trees which explain the basic concepts. Books on TA cover a huge range of topics, too numerous to mention.