New users with less than 5 messages can only answer to topics. You can create new topics when you get to 5 posts. And you can have an access to the private messages system when you get to 20 posts.
BUT be aware that if you post useless messages just to get to this number of posts, you will be banned. Patience is required here, please bring to the forum a real plus, not just garbage.
You also have an edit functionality to modify your messages. Don't post multiple messages at the same place at the same time. If you forgot to tell something, just edit your message. Don't post a new one.
Thank you and welcome aboard.