When you first visit the forums, you'll see the list of categories, like this: You need to click on one of the blue headers to get to the section you want, and then, at the top of the screen, on the right of the blue "breadcrumb" (where it shows Home > Forums in the image above), there's a button like this: Click on it, and you'll be able to create a new topic in that section. I hope that helps
Just updating this in response to an enquiry from a new member: There is no new thread button on this page. In order to see a 'new thread' button like the one in the photo above, you need to go back to the main forum home page (button at the top left of your screen) and select a category. For example, if your Labrador is having behaviour problems, you'd choose the Category: Labrador Behaviour. Once you have clicked on that category, you'll see the new thread button at the top right hand side of your screen