Well essentially all the proof you need comes in the form of three facts.
1) Every living thing must have a parent (theories for the 'first' life on Earth stem from it arriving on a comet to very simple life being formed in a very complex chemical reaction).
2) Some living creatures are very different from some others.
3) Simple animals and plants existed on earth long before more complex ones.
Couple that with our knowledge that animals more suited to their environment survive while other, less successful species or members of the species don't and you have pretty concrete proof.
By evolution I mean, very simply, the development of animal and plant species out of other species not at all like them, for example, the process by which, say, a species of fish gets transformed (or evolves) through various stages into a cow, a kangaroo, or an eagle.
So what, when you look at the many billions of stars out there and then the many billions more planets makes you think that there are none others similar