Welcome to Arduino.
Do a search ( within arduinos search engine top right ) on "countdown days" or " days left " and so on, I am sure I have seen similar projects.
And have a look at the " time" library, I think there is a function to give the days. ( or seconds ) from y2k ( remember that abreviation ?, and all the fears it bought 
Try putting a sketch together, and post it ( select your actual code part of the sketch and click on the hash ( insrt code ) symbol above the text panel , this will keep the posting shorter ) and there are thousands of guys who can help, and dont worry about silly mistakes, nobody will laugh, we all did it !