"Power supply" might be what you are describing. A transformer to drop the 230 vac to something near your requirements followed by a rectifier would deliver 5 vdc in rough form. Adding a filter, which could be a capacitor, will reduce ripple and noise. The voltage will vary significantly with load.
A regulated power supply would reduce the amount of variation and those come in at least two forms - linear regulated power supplies and Switched Mode Power Supplies (SMPS).
With that information you ought to be able to do some research and further define your requirements. Until you've defined your requirements you can't start the design.
"Defining requirements" can be very difficult but you can back your way into requirements by looking at the needs of your application and sharing some of that here. An example might be in defining ripple requirements - understating it can result in electronics that don't work. Overstating requirements can make the task difficult if not impossible. 5 volts to light an LED has less ripple requirements as compared to the supply for a microprocessor.