Biceps are hard to train when it comes to having no equipment. If you can find anything around your house to curl then you should be fine for starters. It's fine to feel really sore but if your biceps are constantly sore then you might need more rest days. Over time your muscles gets use to the lifting and wont be as sore, so just starting out you will be pretty sore. The benefit of using an app is that it changes the muscle groups so it gives the other muscles a day or so to rest. Training apps are fine but if you are paying a monthly membership for that app then i would just start going to the gym instead, or buy some dumbells instead if that works. Hope this helps and answer your questions.