Step 2: Generate your voting transaction while being OFF-LINE

First of all, save this website to your local machine (right click and then choose Save as…).

Next, make sure you know your EOS account name. If you are not sure what it is, use the value extracted from your public key.

Then proceed by choosing one of the following options:

MAXIMUM SECURITY: Copy the file to a secure, off-line computer, which has never been connected to the internet - this gives you best protection. In this case, you should use a pen drive or an external hard drive to port the file to the off-line machine.
LESS SECURE, STILL MUCH BETTER THAN ON-LINE: If an off-line, air-gapped computer is not available, disconnect your machine from the internet (switch off wi-fi, network or whatever you're using). This is less secure, as it won't protect you from malware or key loggers that you may already have, but is still way more secure than doing this on-line.

While being OFF-LINE do the following:

Open the saved 2_generate_transaction.html file in your browser. Your private key is at no point exposed to on-line connections, which greatly reduces the risk of getting hacked.
Fill in all fields. Triple check everything! For chain_id, block_num and ref_block_prefix use the data fetched in the previous step.
Copy or write down the generated transaction, as you'll need it in the subsequent step. Please note that your private key is used to sign the transaction, but it's NOT part of the transaction.