Sometimes a package through USPS may say delivered before it actually is delivered or the package may have got delivered to the wrong address.
Also if you get your mail at a curbside mailbox check around the house as they may have delivered the package somewhere out of sight.
Or if you get your mail at a cluster mailbox they will usually leave a key in your mailbox to a parcel locker on the cluster box.
Then you use the key to get your package out of the cluster mailbox parcel locker.
If you cannot find your package or you don't get the package the next day then contact the local post office that delivers your mail to find out what happened to the package as they can see more than what we can when tracking packages.
A package can say delivered and not be actually delivered.
Sometimes I'll have a package through USPS say the package was delivered but it doesn't show up until a few hours later or the next day after it updates again.
Sometimes the tracking through USPS is not very reliable and sometimes a mail carrier delivering the packages may actually scan it as delivered before the package actually is delivered.
When your package says out for delivery then it will or should be delivered that day but if it's still in transit then it won't be delivered until the expected delivery date.
If you still have not gotten your package delivered then you should call your local post office with the tracking number and find out what happened to the package.
Sometimes a package may get delivered to the wrong address and they can then find it.