3- FORMAT let you insert variables in a string and define properties to it. For example '%d' is used to put an integer into the string, "%05d" let you put a integer that will use 5 characters(The unused characters will be '0').
In the code, "%- 5d" let you put an integer that will use 5 characters(The unused characters will be ' ') and aligned to the left.
0そうだね プレイ済み