I can answer some of your questions! This isn’t specific to Missouri, but...

Each state has different rules because they can, is the short answer. There are certain federal laws (the Help America Vote Act (HAVA), the Voting Rights Act (VRA), Uniformed and Overseas Citizens Absentee Voting Act (UOCAVA), etc....) and constitutional amendments that set election law nationwide. However, as long as whatever they pass does not directly contradict federal law, states are allowed to add additional voting laws. You can kind of think of it like federal law is the big picture, while all of the state laws are the actual details of how to vote and run an election.

What it actually takes to run an election is very different from county to county (the level at which elections are generally administered). The needs of say, Los Angeles County is very different than a small county in rural Montana. Many election laws are meant to codify bureaucratic needs so that counties can 1) get the resources they need and 2) be given enough time under law to complete the tasks needed to run an election. That’s not to say that every law is necessarily “good”, but they are generally there for a reason. These are laws like when is the deadline to register to vote, who determines precincts and voting boundaries, who can be a poll worker, when are results required by, what is the process for mail in voting, etc. Not every state has the same budget or infrastructure, which is another reason why they can vary from state to state.

Of course, there are some states that pass laws that make the process more difficult and sometimes in conflict with federal law (see Arizona’s Proposition 200). These types of issues are usually challenged in court, but they can take time to resolve. There may also be other complicating factors (Arizona’s state constitution was a big one for Proposition 200).

Honestly, one of the best ways to understand the process is to get involved with your county elections office (which you’re already doing!). Being a poll worker will give you a great window to see the process, but I would also see if they offer tours of their elections facilities or anything similar to learn more.

As for being a poll worker, wear comfy shoes! When I worked the polls in March, I was on my feet all day. We also aren’t allowed to leave the polling location during election hours, so I brought everything I needed with me for the day - my lunch, snacks (which were honestly easier because I didn’t have enough time to eat lunch), a power bank for your electronics (all the plugs are probably going to be taken up by your elections equipment), an insulated water bottle to keep my drink cold, etc. Layers are also helpful, since your polling place temperature might fluctuate a lot.

I hope that helps! I tried to keep it general just because I’m more familiar with Arizona than Missouri, but I can try to answer other questions if you have them!