Hi there and Happy New year all

I think one of my new year resolutions is to improve my English. I started to last year but it kinda tapered off... lol I am mostly going to be learning from web sites and places like this

I was thinking of maybe buying a book or two. My question: What is the difference between American and British English? My thinking is that they are pretty much the same and that the only difference is spelling and some small rules of punctuation? Is this correct? Can I learn English from an American book or web site and then just find out the differences later? I would like to know both anyway.
Lastly, anybody have any good book recommendations? My English is pretty basic so I would be wanting something that takes me from that up to a good standard with easy to understand text. Thanks in advance.
Best Regards,
Me.
"Hello. My name is Inigo Montoya. You killed my father. Prepare to ." - Princess Bride.