What are the top five classic science fiction books of all time?
Ender's Game is great, The Hitchhiker's guide to the Galaxy, Stephen King's Dark Tower is long but worth it, 1984 is a good dystopian sci-fi, and so is Fahrenheit 451!
Yes. Those are all top 5 or close to it except for maybe the Dark Tower.  What was the basic plot for it?
It is a multi-dimensional epic about a group of gunslingers trying to stop all of the parallel universes from collapsing. It is a great blend of horror, sci fi, and fantasy and hard to put down!
That sounds like I might like it.  What other parallel universe novels would be good to read?
V. E. Schwab wrote a great trilogy "Shades of Magic" about different versions of London ruled by different types of magic. It is fast paced and the protagonist and antagonist are both appealing, making it an interesting character read.
That does sound good.  Is parallel universe the same as alternate history?
Parallel universes are usually focused on many iterations of the same geographical location involving the same people in different roles depending on the environment of the specific universe. Here everything is happening in the same timeline. An alternate history is one universe that is changed in some specific way. An example of that is this world but if the Nazi's won WWII.
That makes sense.  I've seen some that seem to blur the line.  What are some good alternate history books?
11/22/63 is good book that is about a time traveler who tries to stop the Kennedy assassination. This book is pretty long but definitely worth the time.