Go to one of the many websites that offer free Cantonese and Chinese language learning resources (see the references section). Free Language is a popular site, but Cantonese and Knowledge Hound also have useful resources.
Find a resource that you like. On the Free Language website, click the "Learn" tab located on the top, left side of the screen. Click "Chinese/Mandarin" on the menu that drops down. Finally, choose one of the resources found under "Mandarin Chinese Learning Resources." "Chinese Learn Online Podcast," for example, is a free resource where you learn Chinese by listening to free lessons. On the Cantonese website, all the resources are on the front page, so all you have to do is scroll down and select from one of the many resources. On the Knowledge Hound website, all the Cantonese/Chinese resources are in the Chinese page, so all you have to do is scroll down and find a resource.
Click on one of the resource links that calls your attention and use that resource to learn as much of the Chinese/Cantonese language as that resource can teach you. Use multiple resources; you don't have to just stick to one of them. Some of the resources even allow you to practice speaking, others reading and others understanding.