When you can take your pension pot depends on your pension scheme’s rules - it’s usually 55 at the earliest.
What you’ll get and how you can take it depends on the type of scheme your employer offers you. You can usually take 25% of the money tax free.
If the amount of money in your pension pot is quite small, you may be able to take it all as a lump sum - 25% would be tax free but you’d pay Income Tax on the rest.