In 2010, Oracle Corporation acquired Sun Microsystems, the original company that created Java. Oracle owns the official documentation considered the de facto standard most Java developers reference when coding.
As a new Java developer, you are not expected to be able to navigate this with ease. It is very cumbersome. Consider using Google searches to initially begin navigating documentation. For example, if you want to look at String documentation, enter "String Java Oracle" into a Google search. The more you learn, the more accessible the details of the documentation will become.
Stack Overflow users ask questions about programming and other users answer them. It is similar to sites like Quora. Oftentimes, a question you may have has already been asked. Write out your question, being specific about any error messages and language, and put it into the search bar.
There will usually be a few questions that are similar to yours, browse them until you find something that looks like it matches, then look at the answers provided. If your question hasn't been asked, you can create an account to ask it.
Paste your error message into Google with a little context. For example, "receiving nullpointerexception when trying to access a key in my HashMap."
As simple as it may sound, this will often point you towards where somebody else had this problem, and solved it.
We have found these useful for learning the basics. Some are a bit hard to follow. I recommend typing everything into Atom as you follow along to solidify concepts.
This is a book that drills you on core Java principles. It will take awhile to get through it all, but I recommend taking the time to do it.
The first 16 chapters are available for free here. However, note that this book only works if you type out the code as you follow along. If you take the time to do this, it will help develop your core Java skills and syntax 'muscle memory'.
There are also plenty of great Java books available as eBooks or paper copies. If you are on a budget, check the local library.