My training is in engineering/programming, and my genetics knowledge doesn't much exceed anything taught at the high school level. I am, however, prepared to read college-level textbooks on the subject.

We read this in med school, a bit too wordy for my taste but easy to understand.

I am very interested in how evolution started [...] How did evolution work in the beginning?

Nobody knows for sure. The primordial soup is just an educated guess based on the fact that complex molecules had to arise from simpler ones. This paper focuses on the evolution of multicellularity and briefly references other necessary milestones in early evolution.