Hello,
If you want to learn by making a real game and not exercises, you should first create a GDD (Game Design Document). You can find some infos here : Game design document - Wikipedia
It’s a bit annoying and most of the time we don’t enjoy writing one, but it really helps to stay focus on your goals, and can be a very effective tool to find people to learn/work with 
Then, there is no secret. With UE4, everyone can develop a video game with few knowledge, but the key is to practice, practice and practice. You always have to be curious to solve problems, and to reflect on the different solutions.