How to create a private ethereum network
When planning to write smart contracts you will realize that you are going to spend real ether if you are on the main ethereum network which will cost you real ethers. There is a way around that by creating a private network on various platforms :
Windows: %APPDATA%Ethereum do all your development and testing on private-net. Once you think you are good with your smart code contract you can then deploy it to the main network.