Hello Ernestine, hope you are having a great day and a great weekend , beside a safe halloween
If you want to respond to someone that made a comment on your wall just click on that persons picture and it will take you to their page scroll down to their wall write something and then click submit and you just commentted on their wall.
If you have any questions just leave a message on the page where you retrieve your messages from or their comment wall and we will help you. There is a lot of information here and things to do, like joining groups, discussion boards, joining groups etc.
Please do not be afraid to ask
Welcome and thank you for being a friend
Have an awesome day