At the bottom of the page there is a Post Reply Box where you can type into and add media and/or pictures and go to more options if needed. Then click on the "Post Reply" button underneath. The post box will look like this but have your avatar at the side... If you would like to quote a previous post, click on the blue "Reply" in the bottom right corner of the post you wish to quote. The quoted text will appear in your Reply Box between the words QUOTE as illustrated below. Write your comment below the quote and click Post Reply. The quoted text will appear in a box with your comment below.