There are two basic ways you can log in to the offline application:
Via seed
Via encrypted keyfile (you can generate the keyfile in an offline application before you log in to it)
Login via seed:
Step 1. Launch the offline application
Step 2. On the Login page, in the Seed box, enter your secret seed
Step 3. Click Login
Login 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