1. SNP is a type of polymorphism
2. polymorphism just means that the DNA is "different" due to a mutation for example, a base switch (T and not G for example at a certain place)
3. I think its clear that when you normally have GATC and due to a SNP you have all of a sudden AATC that this change in sequence can cause a disease..
(another example: take for example a SNP in a gene coding for a protein and because of this SNP you get a stop codon rather then a codon for an AA , then what happens? translation will stop and you will not form that protein.. result: disease (or not, its not always the worst case scenario ofcourse)
And that paper might help indeed.