KINDLE APP- Importing Books

I have been given a Memory stick with app 500 books on it.
I have managed to import then on my MACBOOK to a folder 'Books'
I have Kindle App on my MacBook, iPad & iPhone.
The file type is 'Kindle Document'
I am unable to import / copy / move these Books to the Kindle App
If possible I wish to have all these books available in the Kindle Library (or Ibooks)
Please can anyone give me 'step by step' help
Many thanks

Here you go:

1. Delete all the pirated books.

2. Use your Kindle app to buy the books you want.