I see a lot of people posting images of Avatar Designs just like they do with pet designs, but I can't find the generator for them. Where do you go to make like 'dream avatars' or whatever? The picture sources start with https://www.sylestia.com/image_builder_avatar ?

You go to your wardrobe and play around there. If you want to see an item you don't own, click the magnifying glass on the bottom right corner. Click preview changes if you change any colours. Right click to save image/ copy image to post in the forums.