A co-signer is going to sign for you as your backup. If you don’t pay for the loan, then the co-signer is responsible to pay for the mortgage or the property will go under foreclosure.
The cosigner does need to have good credit, income and all that to back you up for your mortgage.
Just having someone as a co-signer for a lot of money with low credit, or, having someone with a high credit score but no income doesn’t help because the co-signer is going to be the failsafe if you don’t pay the mortgage payments.
The co-signer does not have an interest in the property. You own the property and the co-signer is only signing as your backup only if you default to make payments on it.
In most cases, the co-signer needs to be a family member. And they are not on the title.