system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is a "startup" company and how do they work? What is the employee/department structure like?

I live in NYC and many of my acquaintances have told me that they work for a startup. I feel foolish asking for a detailed explanation.

Please and thanks :)
gpt
- A startup could have been formed last week or 4 years ago. 
- They could be working in a garage out of a $1000 investment from a founder, or a 5 million venture capital they painstakingly raised over several rounds of financing after showing steady improvements and meeting the targets they promised they would.
- They could have 2 people working 100 hours a week each and creating a web app, or 50 people working 100 hours a week each and creating the world's first commercial space shuttle.
- Ideally the startup is "flat" and devoid of heirarchy. The CEO can regularly cleans out the sink and loads the dishwasher. The engineer also signs for Fedex deliveries and keeps the bathroom tissue stocked. The intern spends his day helping with market research and making databases of prior patents, competition etc. Come lunch, every one lunches together and discusses their weekend, the game next month, or the concert last week. 
- Dressing is usually casual - jeans, t-shirt, sneakers...sometimes even shorts.
- Focus is on getting your product launched successfully or pleasing a customer, and little importance is given to exactly how many hours you logged in a week. In the same token, startups are more flexible when it comes to employees taking time off. With more freedom comes greater accountability.
- There is a no set path, no formal document that guides you to a certain new process. You explore a lot and frequently have to create a document out of scratch so that future employees down the line may benefit from it.
- Pay usually does not match a comparable job in a Fortune 500 company. However they do make it up by offering stocks. The earlier you join a startup, the more risk you take, therefore the larger chunk of the equity you could hope to bargain for.

Hope this helps. Ask any specific questions. Will be happy to help.