1. Operate with an "encrypted" wallet file, which will require that you connect and unlock your Ledger Nano device before you can view the wallet in Electrum. Effectively, the HW wallet device itself is the "password" to open your wallet file.
or
2. Operate with an "unencrypted" wallet file, which you can open and view all your addresses/balances etc, but cannot SEND any transactions without the hardware device connected and unlocked.
You are given the choice when creating the wallet in Electrum, and it defaults to Option 1.: