Mclaren, I’m sorry but I didn’t realise you were a new user.
When you go into the Forum, click on the heading of the thread you want to read. Underneath each post you will see a link REPLY TO THIS POST. Click on that and the box comes up in which you type your message.
If you are asking a new question, then just type your query.
If you are specifically replying to a person who made a post, I suggest you address them by their user name as the Forum itself does not show which post you are replying to.
I hope this helps. Try copying and pasting your query into the existing Thread, good luck.