How did it start?

Not true. Biological evolution is a process that operates on living organisms, but it matters not one whit how the first living organism got here -- if it even "got here" at all. That being the case, persons can believe in evolution and totally lack a belief with regard to how life began.. I personally don't believe there to be any fundamental difference between "living" and "non-living" matter. Thus, there was simply a point where lumps of matter began a physical process that we as humans call "life." Much like the way water began the water cycle, other forms of matter began the cycle of life.