A volunteer reads a label code one character at a time. code[0] selects the first character; code[-1] selects the last. Indexes start at zero. len(code) counts characters. A single index beyond the end raises IndexError. Strings cannot be changed by assigning to an index.
This is an editable worked demo. Edit main.py, press Run to compare the result, then Submit to check your small change. The next lesson transfers the idea to a different setting.
Change last to select the final character of this different label. The visible result should be R; then Submit.
last to the last character of code using a negative index.