Press Run tests. Your function runs on the three latest past cases (where the answer is known) and once on all the data so far, which is the number you would enter. The data is updated every night.
Return a plain number: return 31.4, or return float(x) when x comes out of pandas. A list, a table or None fails the test.
The tests run in your browser. Some websites refuse requests from a web page, so code that downloads other data may fail here even though it works in Colab. If that happens, the error says so, and you can still submit: at the close your code runs on a normal computer, where downloads work.
Past weeks are practice. Code that downloads other data could see the real answer for a past week, so practice scores are not ranked. Only the frozen run at the close is ranked.