I would suggest that you start by reading a general book about the time by a historian. It could be The Vikings by Else Roesdahl. Understanding the history is vital to understanding the historical sources.
Then I would suggest a book the retells the myths. It could be Norse Mythology by Niel Gaiman.
After that read a book about Norse religion. Myth and religion of the north by Turville Petra are very good, but also quite expensive. Gods and Myths of Northern Europe by H.R. Ellis Davidson could be a second choice.
Then I would suggest that you read the sources, like The Elder Edda, The Younger Edda, Heimskringla, Saxo, Ibn Fadlan and so on. Now you know enough to understand them.
If you want an easy book about modern heathenism/Asatru, then I would suggest A Practical Heathen’s Guide to Asatru by Patricia M. Lafayllve. It is short, easy to understand and has short practices and ceremonies after each chapter and more at the end of the book, both for solitary and group practice.
Everybody also needs a good reference book, and Dictionary of Northern Mythology by Simek is a must-have in any book hoard.
I would suggest that you ally yourself with a local library and second-hand bookshops (along with Amazon dealers and AbeBooks). Get as much as possible second hand or through interlibrary loan.