When we speak or write in English, we use different letters to represent different sounds and words. But in Chinese, instead of using letters, they use characters (pictures that represent words).
So, when someone wants to turn English words into Chinese characters, they have to think about what the words mean and imagine a picture that best represents them. Then they write the character (or combination of characters) onto paper or a digital device.
This process is called transcription, which means taking something from one language and writing it in another language's symbols. It is a bit like drawing a picture of what you are trying to say in Chinese!