A ledger, or other hardware wallet simply keeps your private keys on a device that never accesses the Internet. You only ever put your seed words directly into your hardware device as well, nowhere else.
So when you use a hardware, you connect it to the device with your wallet on to authorise a transaction from your wallet.
Without a hardware device you need to enter your seed words into your Internet connected device. Your private keys are also saved (encrypted) on your device connected to the internet. You use a spending password to decrypt the private key to authorise a transaction.
So if your device with your wallet gets a virus / key logger etc or compromised in any way. Then your funds would be highly vulnerable.
That's the difference.
A ledger, or other hardware wallet simply keeps your private keys on a device that never accesses the Internet. You only ever put your seed words directly into your hardware device as well, nowhere else. So when you use a hardware, you connect it to the device with your wallet on to authorise a transaction from your wallet. Without a hardware device you need to enter your seed words into your Internet connected device. Your private keys are also saved (encrypted) on your device connected to the internet. You use a spending password to decrypt the private key to authorise a transaction. So if your device with your wallet gets a virus / key logger etc or compromised in any way. Then your funds would be highly vulnerable. That's the difference.