向表中添加+符号，显示更多行

Problem : I'm completely new to front end development. I have managed to make a table with some data about university courses using JSONP and AJAX. However, I need to add a new column to the start of each row defaulting to a + sign. When this is clicked, a new set of data describing all the students on the course opens up, and the + becomes a - . I cant yet see the best way to do this. Any advice? I'm completely new to front end devel