Welcome to the AA community!
To start a thread if your on the app simple go to what whatever section you like! Say the freshwater section. Click on the subsection and then on the right hand side top hit the button it will give you the option to start a new thread.
"When creating an aqua scape, strive for the beauty of imperfection, as its art and there is no wrong or right, it's left open for interpretation" James Findley