You start by deciding which areas apply to your business, most SaaS companies begin with Security and Availability.
Then you prepare your internal controls, document your processes, and collect evidence. After that, you work with an independent auditor.
For SOC 2 Type I, they check whether your controls are designed correctly at a specific point in time. For SOC 2 Type II, they verify that those controls actually work consistently over a period of time.
That audit report is what customers usually ask for when they say “Are you SOC 2 compliant?”