ok so!! to reply to a reply you basically just tag the username you want to reply to in the comment section, ex. somebody's username is abc, so to reply to abc in the comments, you write out @abc and then type out what you want to say! but if you want to reply to a reblog, which is when somebody uh reblogs a post and it appears on their blog, just reblog it and type out what you want to say i hope that helps :DD