What does this quote mean the one who is coming after me is mightier than i.i am not worthy to carry his sandals?

This quote refers to John the Baptist acknowledging the superiority of Jesus Christ. He is expressing humility by comparing himself to Jesus and recognizing Jesus' greatness as far beyond his own. Carrying sandals was considered a lowly task, so by saying he is not even worthy to do that for Jesus, John highlights his reverence for Christ.