This is your profile name, which you can use to identify the current profile to yourself, and which won't be seen by anyone else.

The "UI Language" field is for selecting your native language, or the language you want this website to use for menu items, labels, messages, etc.

The "Host Languages" field is for selecting the language the lessons will use to explain things. It typically is your native language, but if lessons don't support your native language, you can choose a different language you might also know, or have multiple languages.

The "Target Languages" field is for selecting the languages you want to study. It might include alternate forms of the language you want to study, such as a romanization, or it might include entirely different languages, allowing you to compare and contrast, if the lesson supports the languages.