"I do qi gong". That's like saying "I do exercise." It could mean almost anything. A person could mean they like weight training, or running, Pilates, CrossFit, or playing a sport such as tennis to work up a sweat. Describing qi gong is exactly like that. I briefly describe the major branches of qi gong in my website: Martial, Medical, Daoist, Confucian and Buddhist.
Within these large branches sprout many more. For example, within the martial branches are Shaolin, Wudang, Mount Ermei and many others. Even these break down into certain lineages. A lineage is a form of kung fu and qi gong that is directly passed down from lineage holder to lineage holder. They contain all the knowledge and mastery of that form. They hold the 'DNA' of that form.
To make matters even more confusing, there are many qi gong forms being taught that may have been part of a lineage and have been taught separately from the original comprehensive format. That doesn't make the qi gong form less effective in and of itself. It is still beneficial but the student may not know it is but a part of a greater style.
Many forms have taken different names and the movements changed somewhat to reflect the style it was taught under. Feel free to youtube "Eight Pieces of Brocade Qi gong" and you will quickly see dozens of pattern variations, speed of execution, sequencing, and even name changes.
For the beginner it all looks overwhelming. "Where do I possibly start?" Well, depending on what you want to do, research the big branches I listed above to see what resonates with you. Many of those branches will have very similar forms contained within them: standing forms, moving forms, sitting meditations, martial forms, physical conditioning or self massage.
My personal suggestion for a moving form is The Eight Pieces of Brocade. It is simple to learn, gentle on the body, encompasses medical and general health benefits and makes a good whole body exercise set. In just about any of it's incarnations, it is a great first form to introduce a novice into a larger qi gong and kung fu world.
Later on the novice can explore other forms depending on his or her interest. That is the beauty of qi gong. You can find the practices that best suit your needs. Use what works for you, discard that which doesn't. Ultimately qi gong is the applications you use to make your own path.