Culture is

• respecting your customers
• respecting your employees
• paying them fairly
• paying them equally, regardless of gender/race/background/country of origin
• giving fair equity in your company (if equity is part of your packages)
• paying people to relocate if you ask them to
• respecting their time off
• respecting their boundaries
• recognizing that we’re humans building things for other humans
• trusting your team
• building your team’s trust in you
• listening to them
• trying their ideas
• working hard for them, not for yourself [1]
• being flexible
• allowing everyone to work remotely if one person can work remotely
• offering the same perks to everyone
• not having one rule for employees and another for managers
• removing pain for customers
• removing pain for employees
• learning what your employees love
• learning what your customers love
• removing roadblocks
• building a learning culture
• supporting hack days
• encouraging hack weeks not hack days [2]
• establishing agreements not enforcing rules
• humans not recruitment
• practices not processes
• completing a task not half-arsing things
• important when your company has 1 employee
• important when your company has 10+ employees
• important when your company has 100+ employees
• important when your company has 1000+ employees
• important when you have no money
• important when you have money
• not cargo-culting
• not blindly following what the competition is doing
• not blindly following what other startups are doing
• listening to what your employees who may worked at other big companies (Google, Apple, Facebook, Amazon, etc) have learnt about working
• listening to what your employees who may have founded a company have learnt about starting companies and growing them
• solving the right problems
• solving big problems
• learning from your mistakes

[1] This idea is described in Australia to a certain extent as mateship of an inclusive nature. It is a term that has militaristic connotations as well for Australians, as the ANZAC story often revolves around thinking not necessarily of fighting for the broader goals (the war), or even the tactical goals (the battle) but fighting because your mates depend on you. In this context, teams that feel bonded and work for each other not individuals (selflessness not selfishness) builds mateship.

[2] Arguably you might even want to consider even longer than that because allowing people to solve problems that are more complete than a random hack. Also, this means that you could consider doing multiple hacks, or a non-work hack and a work hack.