My Account Layout / Buttons / Functions

I want to change the design and the permalinks from my account page for my customer that the links arent clear in the url. The navigation is really bad and not simply as i want, i cant go backwards only with the dropdown menü on the loged in account. I wanted to automatically download datasheets and the invoice in the download section if a customer buys a product in my shop. I would like to have a menu on the side with this buttons and if i click on a button i would like to see the content on the right instead in a new page and empty page. How can i change the layout. I already read in this forum and found this link: https://rudrastyh.com/woocommerce/my-account-menu.html but i dont get it. I can only speak english and german.