How to add UI

Question

how programers turn those codes into an UI

Answer 1

Each language typically has it's own unique API's for creating and customizing the GUI components. Everyone will have their own opinion on which they prefer and you can develop your own by experimentation, persistence, patience++, and practice++. First find the language you want to go for and then try how to videos on youtube. It takes a lot of work to master or even become proficient with GUI's so don't expect things to click right away. After several years, I still find myself learning new things every time I start a new project.