The purpose of multisig wallets is to increase security by requiring
multiple parties to agree on transactions before execution
The normal addresses are governed by a public private-key so one person has the right to spend. Now consider the case where we require the agreement of multiple parties to spend funds. For eg, a corporate account, who can own the keys, only CEO? So this problem can be solved by multisig wallets. So the company can have a multisig wallet with CEO, CTO and CFO as participants and any of the 2 can agree to spend funds out of companies multisig wallet. So no one has full control over the private wallet.
Transactions can be executed only when confirmed by a predefined
number of owners
Multisig wallets are designed so that you can define no of signers ( CEO, CTO, and CFO in the above case) and also no of signatures required to spend funds from multisig wallet ( 2 in the above case). So any 2 of 2 signers can agree to spend funds and can move funds out of multisig wallet. The number of signatures required to move funds is always less than or equal to no of signers.