After you are notified that you are subscribed you can post messages to the list. You can use all lower case if you like. If you want to answer a message posted to the list there are two considerations. If you use your mail programs reply, your message will go to the entire list. There are about 40,000 discussion lists.
Topics range from the esoteric to the bizarre.
Pick a topic and there is a real good chance you will find a list specializing in that subject. If you have any questions, drop me a note.