Hello Janice and welcome to the group. There are several different ways to respond/reply to greetings and messages. It all depends on how they have been sent.
1) If you get an e-mail informing you that a member has sent you a 'Greeting' then that is all it will say. To respond to that greeting, you can either click on the link provided in that e-mail or go to that members profile page by clicking on their 'Nick name'.
On the bottom left hand side, you will see a box with a list of options, ie: Send a greeting or Befriend are just a few of them. Just click on either of those. Personally I prefer to use the befriend option as this allows you to send a small message to the recipient, where as you don't get that option if you just select 'Send a greeting'
2) If another member sends you a message via the site e-mail, then this will be indicated next to the 'My mail' link situated in the green banner at the top of the page, just under where it says 'Hello Jojan'. If you scroll down to the bottom of the message it should give you the option to reply to that message.
These sorts of questions have been asked many times before so you are not on your own,and you may find the answers to many of your questions in the Forum, although you may have to search for them.
I hope this helps for now, please feel free to e-mail, greet, befriend me if you wish to try them out. Happy writing
Laurie