To participate in the Shotgun community, sign up to the upper right 
.
To be a part of the conversation, select any blue Reply button 
. That will open the editor panel at the bottom of your browser where you can preview your reply.
To reply to a specific post in a topic, simply:
a) Select the Reply button 
at the end of each post, and your reply will be linked to that post.
b) Select text you’d like to quote, and then Quote
. This will open a new reply draft with the quote inline.
To post a new topic, simply select + Topic 
on the upper right. From there, you can select the category the topic should fall within. If you’re creating a topic in the context of a category, that category will autofill.