The next thing is to let your ideas flow. Before you start writing you might want to start with just brainstorming ideas about the topic that you can talk about. You have your topic, then what are you going to talk about in that topic.

For example: Cats is your topic. Lets say you decide to talk about your cat and your experience. Well, what about cats do you know? What have been your experience with cats, good and bad? What advice would you give to others?

All this can go into the same article. Just brainstorm what you know and the main points you have about the topic.