In order to purchase an annuity, all of your existing funds in your pension account must be cashed in. There are different types of annuities available, but in all cases an annuity guarantees you a fixed income for a period of time.
The amount of your annuity income will depend on a number of factors, such as the amount of money available to purchase the annuity, your age, the type of annuity you buy, and interest rates at the time of your annuity purchase.
If you have a spouse at the time of your retirement, your annuity must (by law) include a joint and survivor benefit. This will ensure that if you die before your spouse, the annuity will continue to pay your spouse a fixed, lifetime benefit.