The list is organized by topic. First, find the aspect of a painting you wish to talk about (for instance the colors), then see which words match or fit with what you're thinking. Start by putting it into a simple sentence such as this: "The [aspect] is [word]." For instance, "The colors are vivid." or "The composition is horizontal." It'll probably feel awkward at first, but with practice, you'll find it gets easier and more natural. You'll soon expand into longer sentences!
At times it may feel like you're stating the obvious, something that would be immediately evident to anyone looking at the painting. Think of it as answering the question "How do I know that you know except by your telling me?"