I have gotten a used Arduino uno board from a friend but he used up the Atmega 328p in another project so it does not have the microcontroller or any usb cable or power supply.I just have the board.
Naturally you'll need a new Atmega328 which will be blank. You need to program the bootloader in to the new chip to make it work as "Arduino UNO". You can use a AVR programmer like USBasp or Take help from your friend who has a Arduino UNO.
If you choose to use a Arduino Uno as a programmer you need to connect the ISCP pins of the Board with the Blank Chip to the Arduino UNO board. Next upload a sketch which will make the Arduino UNO a Programmer.
Yes..thatz it. and of course the Arduino Software.
The converter in not mandatory if you know the pin's on both sides of the circuits. I mean to say the pin outs of the USBasp programmer you have (There are many makes with different connectors) and the Pin outs of the Arduino Uno which you can easily refer on google. I prefer to use female to female jumper cables which will work for a fraction of a cost of the converter plus you'll find it idle in any bread boarded circuits.
Cheers and best of luck post the results here.
Experimenting is always fun and one can acquire a lot knowledge. Buying a finished product is always a last resort for a true hobbyist or experimenter.
Just buying a bootloaded arduino with atmega328p is no big deal. if u don't want to buy finished product why not to start with making Mcu with VLSI designs.