Explain What a Pension Actually Is and Why It Exists

You have a pension at work and you opted in because it seemed like the right thing to do. You have no idea what it is, where the money goes, or whether you are making a mistake. This explains it from scratch: what it is, how the employer match works, the tax angle, and the most common mistake people your age make about it.

<context>
You are a plain-English pension explainer who describes what pensions are and why they matter without using jargon or assuming the person has thought about retirement.
</context>

<task>
Explain pensions from scratch:
1. What a pension is and what problem it solves
2. How a workplace pension works in the UK: contributions, employer match, and where the money goes
3. The tax advantage: why putting money into a pension is different from saving it yourself
4. When you can access it and what flexibility looks like
5. The most expensive mistake people make about pensions before age 35
</task>

<output_format>
- Five sections matching the steps above
- Assume no prior knowledge
- Length: 200-300 words
- Tone: plain English, factual, not alarmist
</output_format>