I have no idea about String Theory, I was hoping someone here might!
I do think though itís probably one of those things that makes more sense when you understand what went before it and what itís trying to overturn or react to.
This book by Bill Bryson (A Short History of Nearly Everything) is supposed to be great (not yet read it but have heard great things) for introducing the major theories about life, the universe and everything that String Theory is reacting to but in a more accessible way than diving into say diving into Stephen Hawkingís Brief History of Time (also on my list once I have read the Bill Bryson!). That said I think there is nothing wrong with diving into the major books intended for people with some background in the area, they are just stacks of paper with words in after all and sometimes some of those words stick, give it a whirl!
The Bill Bryson book:https://en.wikipedia.org/wiki/A_Short_History_of_Nearly_Everything
If you are interested in Philosophy at all, I have read and recommend this book by Jostein Gaarder!https://en.wikipedia.org/wiki/Sophie's_World
Itís aimed at teenagers (the philosophy it tells you about is kind of set in a mildly annoying story) but I read it in my mid-thirties and I couldnít believe no one had told me about this stuff. I ended up doing a BA degree in Philosophy as a mature student, something I thought would never happen because despite doing OK with my GCSEís (apart from Maths which I only got when I did a course later as an adult) I totally failed all my A Levels due to depression. I did then much later do an A Level in Psychology as an evening course so that helped, but now I think I would have to do an access course to get on. Anyway I loved it and it went really well so I then did an MA. That was very hard because I was working full time and studying and attending lectures in the evening and weekend but I got through that. I then got a scholarship to a PhD which I am completing now and I canít believe Iím here frankly. Academia is a very strange place, itís full of people who got things right all along, who never failed anything and long term itís not really somewhere Iím happy.
But what Iím trying to say is Iíd encourage anyone to try and find out more about something they are interested in and attack even those big scary books. Loads of these big intimidating books come with really helpful study guides anyway so give them a go. Itís not wrong if you a read a bit and donít understand, sometimes it means looking something up, something it means having good hard annoying think, sometimes it means carrying on anyway because later it becomes clear but that gap and making the leap in understanding is a very important part of the process. Sometimes though you just have to throw it on the floor and walk away and then later, (sometimes days sometimes years later) itís like your brain has carried on chewing it over and it make sense now. There is no one who reads these things straight through and gets them first time although practice makes it look like that from the outside. Itís not necessarily about finding better ways to put things either (although finding the problem put in someone elseís words can really help) itís just that these are big ideas and they canít always be swallowed whole. Good luck and enjoy!