e-book download

Sunday Night late, I was successful in downloading an e-book. I have wanted to see how this worked but just not taken the time. The first attempt put the bookby agatha christie on my card but I was unable to read it and have been unable to read it. The second attempt was successful! Another Yea! It is on my home computer and I started reading it last evening. I did not find it easy to use. I am not sure where to put the book since many people share the computer at my home. Once Adobe digital was downloaded, does it stay on my computer ? This is my next discovery. Reading a book on the computer screen is not enjoyable for me. Over time I guess this could change.