Question about the DUNE books

So yeah I was interested in reading the books but whenI went to my library they only had the second one, The Machine Crusade and the third one, so I borrowed the book, question is, should I read the first book before reading the second one, would I still understand?

Hmm?

of course like any book series if there is a series of books you should read them in sequence.  
 
dune 
dune messiah 
children of dune 
god emporer dune 
heretics of dune 
chapterhouse dune 
 

Sounds like the books that you picked up were the 3 prequels written by Frank Herbert's son that details events thousands of years before the events of the original series, and yes you'll want to read the first one before reading the second one.  Aside from those 3, he also wrote another 3 prequels to the original series called House Atreides, House Harkonnen, and House Corrino.