im new in arduino world first. i like to use arduino for my project but i am a little bit hesitate on using it because im not sure with this: if you already have a program or sketch and you already burned (or installed, i dont know what's the correct term) it to the arduino board, will i be able to reverse the process again and clear my arduino board like the first time i bought it?
i do make mistakes frequently so i have to make sure that i can redo/undo all the mistakes i have done in the arduino board....
PS.. what are shields by the way, i keep on hearing them
Yes, you can flash a bajillion different Sketches to your Arduino and only the latest Sketch you flashed will be on it. No need to worry about your Sketch not working 100% the first time, fix up your code and flash it again until you're working correctly.
Shields are specialized boards that stack neatly onto your Arduino that make doing different tasks easier. IE: MotorShield, WaveShield, ProtoShield, EthernetShield... will help you interface: motors, wave (audio) files, prototype circuits you've built and ethernet (internet) connectivity, with your Arduino respectively.