Programs like Word, Open Office, or even Google Docs work fine.

If you want more features, you can go with Scrivener, which gives you a great overview. That is helpful when you write books with more than three chapters.

Scrivener can show you a chapter alone, or even a scene alone, if you write fiction. It can also show you an index card overview, and you can move the index card around.

The electronic version should be in a specific format, for example ePub, and the print version should be a PDF file.

KDP (Amazon’s self-publishing platform) offers an addon you can use with Word. With the help of that addon, you can format your manuscript, so it looks nice both in the electronic version and in paperback.

Scrivener can be set up to format your books, both for the electronic version and the paperback, and once it is set up, it only takes a few clicks the next time you want to format a book.

If you create your own covers, you can use an online application like Canva. It has limited possibilities, but it is good for beginners, because it is click and drag, and you have your design.

For more professional covers, you need a stand-alone program like Adobe Photoshop or Illustrator, or Affinity Photo or Designer.

If you are on a shoestring budget, you can use a free program like Gimp.