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?
Right.
But you have to get the private key to this offline wallet anyway ( this is where I found paper wallets pretty unhandy ). You have to scan the QR code ( if you don't want to type it in by hand) which I found the most easy way to leak (revealed QR is dangerous IMO). And then you have to get the signed tx to online device.
So my advice is to import the wallet to online device spend the coins, throw the paper wallet away and make a new one.
Being extremely cautious is always good. Especially when dealing with bigger amounts.
If you really have a bigger amounts I highly recommend you to purchase hardware wallet (it's much easier to use and even more secure)