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?
That is correct. You need to have a bitcoin wallet, like Electrum, installed on your offline computer.
Then you can import your private keys and sign a transaction.