On my first day, I'd expect the following in no particular order:
- Introduction to co-workers and maybe what they're working on (high level, nothing weedy)
- Introduction to workstation
- Shown around the office (restroom, supplies, kitchen, points of interest)
- A mound of HR paperwork to fill out
- How to set up email, messaging service, phone, video calls, etc
- Lunch out with my immediate co-workers (best if employer communicates this in advance for a host of reasons)
- If time, but probably day 2: introduction to the tech stack/workflow by co-workers
- If time, but probably day 2 : access to any documentation related to first assignment presumably coming in the next few days
In my experience, the first day is usually spent getting settled in with no real work getting done. I'd expect it to be a welcoming experience with people dropping by to say hello and a bit of breathing room to settle in before the grind kicks in a few days later.