Borrowbox and RBdigital are the two audiobook apps my library use (Nottinghamshire). Search audio books on your county council website to find the ones used by your library.
These are completely free audio books. You borrow them for 30 days, as you would a normal library book. Set up an account on the app using your library card details.
All you need to use is a digital device that you can have apps on - so any smartphone or tablet. Plus headphones if you want to listen privately.
Lots of the usual big authors and best sellers on the apps - all free.
Audible, on the other hand, is not free. It's £7.99 per month and for that you get one book a month. You then own that audiobook forever, rather than just borrowing it like the library. I used 6 audible credits to buy (and own) the Harry Potter series of books, just because I wanted to be able to listen to these over and over again So was happy to buy them. But for normal every-day easy reads that you'll probably never listen to mire than once, better use the library app and not pay.