The short answer: only a driver’s license.
Unlike taxi services which are heavily regulated, there are no certified licensing programs for rideshare drivers. All a driver needs is a valid driver’s license and auto insurance. After meeting a few other company-based requirements, drivers are free to transport clients with no additional training or experience.
Initially, this resulted in many of these services being banned as unlicensed taxi companies. However, bans have since been lifted, leaving the companies free to operate.