If you are completely new, I would recommend to first follow this tutorial series:
This is the best UE4 intro series I’ve found on Youtube and I wish I would have known about it when I first started.
If you want something more complete, check out this Udemy course for $10 - https://www.udemy.com/unreale4/?couponCode=BEUNREAL
The reason I recommend this is because you need to understand UE4’s basic workflow and tools before you can plan your game. Once you have a good idea of the basic tools (like creating basic materials, importing and implementing basic animations, using Blueprint, etc) it will be a LOT easier to start your game prototype.
Start with the Blueprint Thirdperson game template and start adding functionality via Blueprint. Here is a small list of easy things to add:
Add melee animations
Basic HUD with health and stamina
Another NPC with basic AI (a bit more advanced)
Alternatively, you could start with a more robust template like my free Action Platformer Template:
-> Link to Thread <-]([FREE] ThirdPerson Action Platformer - Community Content, Tools and Tutorials - Unreal Engine Forums)
This already has a lot of the basic functionality you will need to start your game, HOWEVER, if you go this route, take the time to look at the code and understand how it works so you can then modify it to your liking :).
The goal should be to learn as much as possible.