What is the actual use of it though? & Doesn't it kind of contradict evolution?
Edit: the answer for that is probably too long for this forum and not so simple I'm guessing lol
I don't mind going into it really, I'm in the process of procrastinating like a boss at the moment, so I'll look to do anything to avoid studying.
So, to make a start, let's look at the classical definition of entropy as described by the second law of thermodynamics. In an isolated system will over time reach equilibrium with its entropy at maximum. That is to say, in an isolated system entropy will always increase.
There are many definitions of entropy. The most simply understood of these is a measure of disorder. A few examples would be if you leave an ice cube in a glass of water the system will eventually achieve equilibrium with the ice cube melted or if you add milk to your coffee the two sets of particles will mix until they're pretty much exactly evenly distributed.
Taking these examples will allow us to illustrate a few things about entropy. Firstly, the idea of order. The atoms in the cube are more ordered than that of the liquid water. They're have less freedom to move and exist usually in a repeating lattice formation, whereas the liquid just moves about essentially randomly. Secondly, the idea that entropy always increases. This is a common sense kind of thing. You can't unbreak the glass and an ice cube wont just magically form out of a glass of water (oddly enough, both of these things are possible using the more accurate statistical concept of entropy which I can go in to if you like, but the probabilities are so tiny that the odds of these things happening in a universe of the age of ours is essentially 0).
Now you might say "but we can make ice cubes out of liquid and we can make well shaped glasses out of rougher materials. Surely that goes against the second law of thermodynamics as order would increase and therefore entropy would decrease?" This is where our definition of a system becomes important. A system is essentially divided into to parts; the system, and the surroundings. While in our system the entropy decreases, in the surroundings it increases, meaning that total entropy increases.
Let me draw a simple analogy. We make a glass. We've taken some rough materials and put them in an ordered state. Entropy goes down. But to do so, we have to heat the materials up and work them. For the heat we burn a fossil fuel. When we burn oil for example we change it from a complex molecule into more simple parts, namely carbon dioxide, water and sometimes oxygen, as well as some other nasty stiff. Thus it becomes less ordered. This disorder we create to supply the energy to do the work to shape the glass will always be higher than the order we create making the glass. Thus, entropy overall increases.
To deal with your point on evolution, the same logic can be applied. Through evolution more ordered systems are being created. However if we take our total system to be the solar system and the work being done to be fusion, then we can say that entropy is increasing, Remember that thanks to our old buddy Einstein energy and mass are equivalent and interchangable, so as we do this we reduce the total amount of free energy and the ability to do work.
Hope that helps.
thanks for explaining that - I wish I could study Physics at university level it would be so interesting 
