Entering your private key into an online computer kind of defeats the whole purpose of cold storage. The best way is to sign a transaction using an offline computer, copy the signed message and then broadcast it.
It is best to be paranoid while dealing with bitcoins.
Thanks! So to sign a transaction using an offline computer, I would need a bitcoin wallet installed on Offline computer. Right? If I just have a paper wallet, then?
Yeah you need to have a electrum or multibit wallet installed on your computer. Once after this you can further process by importing all the bitcoin towards the particular wallet using the private keys and once again sign the transaction, which is the easiest process.