1. And if there really is evidence ...
Yes, there is a mountain of evidence in support of evolution. The fossil record, the universal genetic code, and the fact that all living organisms use DNA as genetic material are all powerful pieces of evidence in support of evolution.
2. what this mean for us?
It means we share a common ancestor with all other living organisms on earth, and that includes bacteria, fungi, plants, protists, and animals. That means our ancestor was at one time a bacterium. Later it became a fish, an amphibian a reptile and a shrew-like mammal. As recently as 65 million years ago, our ancestor was a shrew-like mammal. Primates did not evolve until after the dinosaurs were wiped out by a giant meteor striking the earth at high speed. Monkeys did not exist until 35 million years ago, and apes did not exist until about 25 million years ago, and modern humans did not evolve from H. erectus until about 150,000 to 200,000 years ago.
3. Does this mean that we are just mutated chemicals?
No, we are a lot more than that. We are made of chemicals of course, but what makes us living is that we have all kinds of regulated chemical reactions going on inside our cells and bodies. For example, we make proteins that will be stuffed into cells which then become part of the outermost layer of the skin. Mere chemicals cannot do that. We do that using cells and cells make the chemicals we need from recipes contained in our genes. Our body is made up of billions of cells, which are chemical factories.
4. Are we just animals?
We are more than "just animals." We are of course part of the animal kingdom. We are one species within the animal kingdom, but we are the smartest animal that has ever lived, bar none. We are unequaled in the things and tools that we have made. We invented and made computers, and we communicate with other people on any part of the world wherever internet and telephone signals can reach. No other species can do that.
5 If the answer to these questions is yes, then what is the purpose of our existence? We just exist because we exist?
Existence has no "purpose." All organisms have one goal, and that is to live long enough to reproduce themselves. Many insects for example only live a single day as adults, and they die after mating and laying eggs. They are here and they will be here as long as they can keep on passing along their genes and to avoid extinction. The sun will run out of fuel and it will become a red giant after another 5 billion years or so. When that happens, the earth will be engulfed by the sun, and everything here on earth, including all the rocks, mountains, water, buildings, fossils and all living organisms will be vaporized and destroyed. In the end all that happens on earth will be erased and there will be no record of it.