An simple example of multisigwallet working mechanism, may have many security bugs, DO NOT use this code in your products.
When you sign a transaction in a 2/3 multisig model, you hold two signer (two private keys), and the third party hold one in the cloud. You can create a transaction and regard the third party signer as a Multi-Factor Authentication, so this can improve the transaction security when some one steal away your hot wallet key.
When you lose your hot wallet key and can't recover it from mnemonic words, don't worry, you can use the cold wallet key as a signer and the third party signer to sign a transaction to transfer your assets in the contract to another address (account address or contract address).