Via encrypted keyfile (you can generate the keyfile in an offline application before you log into it)
Log in via seed:
Step 1. Launch the offline application
Step 2. On the Login page, in the Seed box, enter your secret seed (you can view your seed in the Account Settings)
Step 3. Click Log in
Log in via encrypted file:
Step 1. Launch the offline application
Step 2. On the Login page, click Open encrypted keyfile
Step 3. Select the previously generated keyfile from your computer
Step 4. In the Password box, enter your password for the keyfile decryption
Step 5. Click Unlock file