First of all, we have a dream diary: It is here where you take down notes about your dreams (if you can remember them, of course). If you do this regularly, you will train your brain to remember dreams and soon you will be able to remember your dreams in detail almost every morning. I can confirm this is true based on my own experience.
The more exciting part concerns lucid dreams. In a lucid dream, you wake up and continue dreaming at the same time. Get this: You are fully aware that you are dreaming and thus are able to take full control of your dream. You will be able to do whatever you want, visit any place, or meet any person.
The easiest way to achieve lucid dreaming is to perform reality checks during the day. For example, you can press your right finger into your left palm and imagine piercing your hand with your finger. Of course, this doesn’t work in the real world.
If you regularly practice this, sooner or later, it will happen in your dreams. This is where the reality check will tell you that you are dreaming. The same idea in Christopher Nolan’s Inception was described as a ‘totem’. At this moment, you take control of the dream. You can find detailed instructions on how to do this in the app, with the app sending you regular reminders to perform Reality Checks.