Hi Sandy,
No, the replies don't need to have a title, but sometimes they can help. e.g. if you're replying to someone in a long thread, sometimes I just put "for so-and-so" in there or maybe a description such as "regarding medication". Hope that makes sense.

If you're making a new thread though, there does need to be a title.
The more descriptive the better I suppose and not too long.

When replying to another post in a thread there are also Icons that can be put in the space where the title can go.
The Icons are just under the Reply box.

Posts can be edited as well.

FAQ - Reading and Posting Messages

that's from the Frequently Asked Questions - FAQ

You're doing fine.