Make sure you are logged in and your account is fully set up.
Then click +Post and choose the Livestock category.
If you want to sell livestock, choose the For Sale option, if you want to buy livestock, choose the Wanted option.
Follow the questions through, and be sure to include a good description and photo!
Then, at the bottom click Post Listing. If you cannot press this button, you will have missed something out, maybe ticking the Terms and Conditions.