Plain answers
What exactly is a system?
A system is a reliable way to make something happen. That's the whole definition. Everything else is detail.
A system can combine almost anything
People, software, information, instructions, automation, physical tools, devices, media, decisions, and repeated actions. The mix depends on the problem — not on what some product happens to sell.
A sticky note on the door saying “keys, wallet, badge” is a system. So is a complete learning platform with learner accounts and reporting. The difference is scale, not kind. Both exist to make something happen reliably instead of by luck and memory.
That's why no job is too small here. A reminder that actually works is a legitimate build. So is an organization-wide operating system. They're rungs on the same ladder.
The progression
Climb the ladder
Select a rung to see what it means and what it looks like in practice.
A reminder
The smallest honest system: something that reliably surfaces the right information at the right moment, so a human doesn't have to remember to remember.
In practice: the checklist that fires before every event, so nothing rides on one person's memory.
Try it on your problem
Pick a familiar frustration
See how it could become a system. Close is close enough — the real project usually shows up in conversation anyway.