Let's say a protein is encoded on DNA as ATC.CAT.CGA.GGG.CAG
Let us say a point mutation occured and it became ATC.CAT.CGA.AGG.CAG
Same amount of information, different protein most likely (I don't have my codon cheat-sheet handy).
Now, let's assume that during duplication, the two strands get stuck end to end. This is another known mutation. So now we have ATC.CAT.CGA.AGG. CAG.ATC.CAT.CGA .AGG.CAG ... two copies of the same protein. So long as one remains functional, the other is free to mutate via point mutation, and the result may become useful. This is new information.
Via point mutations, you might end up with
ATC.CAT. CGA.AGG.CAG. ATG.GTT.CGA .ACG.CAG
And find that both of these proteins are useful for protein synthesis... but the second one is BETTER at it. So organisms with that gene will have a lower energy requirement and thus be better able to survive in the same environment.
Believe it or not, one of the proteins involved in your ability to form a blood clot is provably related to a digestive enzyme... this is likely how it happened to get changed around.