I cannot understand the below part of a python program.

Question

while len(word_letters) > 0 and lives > 0:
        # letters used
        # ' '.join(['a', 'b', 'cd']) --> 'a b cd'
        print('You have', lives, 'lives left and you have used these letters: ', ' '.join(used_letters))

        # what current word is (ie W - R D)
        word_list = [letters if letters in used_letters else '-' for letters in word]
        print(lives_visual_dict[lives])
        print('Current word: ', ' '.join(word_list))

the part which i am finding difficult to understand appears at 32:15 of the above video.
i don't know how to highlight a part of a code while posting a question on this forum. this is my first post.
if someone can help than i would be very grateful.