In this YouTube video, Catherine shares four techniques for using ChatGPT to improve English skills. Firstly, she teaches viewers how to write a business email, including providing keywords to command ChatGPT and not relying solely on its content. Secondly, by asking ChatGPT to define words and provide example sentences, viewers can improve their vocabulary. Thirdly, they can practice grammar through ChatGPT by asking it to correct their sentences or provide natural-sounding alternatives. Additionally, viewers can practice conversation skills with ChatGPT through simulations of various scenarios, like job interviews or small talk, while asking for example sentences for better responses. The video concludes by advising viewers to use ChatGPT as a reliable friend for improving their language skills.