Right now, if you're struggling with basic comprehension, don't worry about any of the history or the finer points of language. You need to practise boiling it down to the basics (a good technique for any text, though).
Ransom is a story about two guys (Achilles and Priam) who are really big and important. Achilles is a famous warrior and Priam is a famous king.
Achilles isn't allowed to be soft and human because he's a warrior, and Priam isn't allowed to be soft and human because he's a king. So Achilles can't be sad about missing his son, his farm and his best friend (who gets killed); and Priam can't have a proper fatherly relationship with his kids or enjoy the small things in life that regular people do, like cooking and eating and spending time outside chatting. Achilles has to be a "warrior" and Priam has to be a "king".
The thing is, Achilles and Priam are at war, and Achilles has the dead body of Priam's son - and Priam would like it back so he can bury it. The whole 'being at war' thing doesn't seem to be working, so Priam gets this crazy idea to just go *ASK* Achilles for the body - man to man, father to father, human being to human being. So he does, and it works.
Of course everyone goes back to killing each other and being warriors and kings and everything afterwards - but for a brief moment they're just two guys connecting with each other. So we know it's possible. Human beings may be dumb and prefer conflict and status etc in the long run instead of getting along and being real with each other, being human... but maybe we can learn our lesson bit by bit?? Maybe???
And that's the story. Obviously it's missing detail, but you fill that in later. A body has a skeleton first; then it has muscles and organs; then it has skin and hair; then maybe it puts some clothes on. Get the basics first.
A tutor can be a real help with this kind of thing, but in the meantime I suggest you do the following:
Take out a piece of lined paper. Have it next to you. Read the first passage in the book - write down what happens (ie "A guy is standing on the beach"). In really basic language that you 100% understand. Then read the next bit until something different happens - when something different happens, write that down. Repeat.
It will take a fair while to get through the book, but you need to *process* each paragraph/section before moving on to the next or it will all be a big blur. If you summarise all the things that happen in really basic language that totally makes sense to you, you will have your own 'version' of the book that you can read through afterwards to help it make more sense. Then, once you understand it, you go back to the original for some detail and language.