I am new to UE4 and I want to try to make an open world game similar to something like fallout with levels and quests, but also like ARK survival evolved where you can create items, built structures and generally do whatever you want, is it even possible on UE4? and if it is, how would I be able to do it?
ARK was made in UE4, so that should answer the question whether it is possible.
Large games like that take entire teams require infrastructure and process to complete. It is not possible to do it by yourself. Because of the nature of the question, asking if making X game is possible in UE4 it shows that you are not experienced in game development, with more experience you would be able to evaluate the engine on your own to see if it meets your specific needs.
I recommend you start with making small projects, not even complete games. Add a weapon to Unreal Tournament for example, or a game mode. You need to get the experience first of making parts of a game, then can build up to making an entire game. Even “small” games can take years to complete if they are done by small teams not working full time on it. Because there’s such a high time investment in making a complete game, you are better served to spend your time on something that you can complete much faster and see your progress.
It is very possible, but it will take a lot of work.
To reach that goal you need to start small. Begin with the tutorials provided by Epic. Make a couple of simple games experimenting with one of the mechanics you want to learn in each of them.
As you mentioned ARK, maybe you should try making a mod for it first (and learning UE4 while you do). Even then, start with something really simple.