Be Patient. Even though the Yang 24 Form style of Tai Chi can be completed in about 5 minutes, it's going to take some time to learn. The movements are simple, but there's a lot of subtle things going on that will take time to memorize and perfect. Take the time to notice the position of the head, the hands and feet, as well as the body. Just about every part of the body is part of the Tai Chi motion. Watch the video closely. It's also going take some time develop the muscle and balancing skills to get to the point where you can perform the movements without being jittery or having to catch your balance. No one rides a bike on the first try. Tai Chi takes practice to do smoothly. The good news is that even the learning process is beneficial.
Don't try to learn it all at once. As mentioned above, while the 24 Form is only 5 minutes long, there's much to learn. If you try to learn all 24 forms at once, you're either going to frustrate yourself or miss the little details that make Tai Chi so graceful and fluid. Professional classes often progress by teaching one new form a week. You can go a faster, especially if you practice every day for 15 to 30 minutes. But you should only advance to new forms after you're comfortable with the previous ones.
Don't forget to review! Chances are you will break up the lessons into learning one or two new forms at a time. This is a great way to progress. Just be sure to set aside some time to review the previously learned forms. It's easy to forget the earlier forms while learning new ones if you don't set some time aside to practice all the forms you've learned. Be sure to run through all of the forms you've learned from start to finish to polish any rusty spots that may have developed.
Don't isolate the forms. You will probably be tempted to isolate each form while trying to memorize it. This is fine when first learning the new form, but you should begin to practice the new form by performing the previous form or two so that you get a feel for how the forms flow together. For example, if you're trying to learn form 10, practice it by performing forms 8 and 9, then smoothly moving into form 10. Don't just do form 10 by itself. Keep doing this until it becomes automatic. You need to keep practicing if you're having to stop and think about what form comes next. Advance to the next new form only once you can do all of the previously learned forms without thought.
It's supposed to be slow. The application (at normal playback speed) is showing the correct tempo for performing Tai Chi. It's supposed to move that slow. You can move faster to squeeze in more repetitions when learning new forms within a limited time span. But set some time aside to move at the proper slow speed. The slower speed does a better job at developing coordination and balance.
Focus on the motion. The meditation and relaxation part of the Tai Chi comes from tuning out the outside world and tuning in to your own body. Concentrate on your balance and how smoothly you're moving. Listen for flaws in your motion/balance and work to correct them. Some practitioners of meditation focus on a burning candle to help clear their mind. In Tai Chi you focus on your own body.
It's OK to cheat a little when learning. Tai Chi is going to ask your body to move and balance in ways to which it's not accustomed. It's a new motor skill which will challenge you. Chances are you're going to feel awkward and clumsy when you first start Tai Chi. That's normal. You can make the learning curve easier by modifying the moves to accommodate your level of development. One of the first things you're likely to run into trouble with is doing the 'bow stance' which requires standing with a deep knee bend. The bow stance is frequently used in the 24 Form as a transitional move from one form to the next. Your knees may not be comfortable with the bow stance at first. You can cheat by standing a little higher to take the pressure off the knee. Over time, your knees will get stronger and you'll be able to sink into the full bow stance. You can also take smaller steps if you're having trouble with holding your balance while moving from one leg to the other. You can work up to the larger steps as your balance skills improve. (You can take the crash course in improving balance by moving very slowly when performing the portion of the form that's giving you trouble. Keep doing the slow motion and practice making tiny shifts in your weight to keep your balance. Your balance will improve if you keep doing this.)
Use good form. Even though it's OK to cheat a little while waiting for your body to adapt to the demands of Tai Chi, you should still try to keep good form. Be sure to practice good posture and do your best to emulate the movements shown in the application.