cd is short for "change directory": it is how you walk from one folder into another. Notice that it printed nothing at all. In the terminal, silence means success: commands only speak up when they have something to say or something went wrong.

Once you are somewhere else, ls lists something else: the files inside notes. Same command, different answer, because ls always talks about where you are standing.

Watch two things change as you walk: the prompt (~ becomes ~/notes) and the file tree on the left, which highlights the folder you are in.