can information be retrieved once I have done a factory reset

If your Mac is using an SSD, then when you erase the whole physical drive it will also make it impossible to recover any data due to how SSDs work. If your laptop uses a hard drive, then first turning on Filevault as previously mentioned by others and letting the encryption process finish will protect your data so when you erase the whole physical hard drive, then it will destroy the encryption keys so the encrypted data can no longer be accessed (no need to unlock Filevault when erasing the whole physical drive on Intel Macs). Hard drives are where you need to be careful since a simple erase will leave most of the data intact unless the hard drive is encrypted or the hard drive is written with a single pass of zeroes (Apple no longer provides a simple way to write zeroes to the hard drive since that process will add unnecessary wear to an SSD so using Filevault is the easiest option).

If you have a 2018+ Mac with a T2 security chip or an M1 CPU you have an additional option if you have access to another Mac running macOS 10.15+, then you can "Restore" the firmware which will reset the security enclave and perform a clean install of macOS using Internet Recovery Mode.

Revive or restore an Intel-based Mac using Apple Configurator - Apple Support

Revive or restore a Mac with Apple silicon using Apple Configurator - Apple Support

Once you've done this there is no retrievable information on the computer.

What to do before you sell, give away, or trade in your Mac - Apple Support

Ok i was told anyone very good with computers could retrieve personal info & i do not want that

That's not entirely correct.

If you encrypted the startup disk with FileVault, all you need to do is erase it according to the instructions BobTheFisherman provided.

Use FileVault to encrypt the startup disk on your Mac

If you have a newer Mac, that encryption is already performed in hardware.

So... a definitive answer depends on the model Mac you have, and (depending on that answer) whether you chose to encrypt its startup disk.

Yes. Restore your data from your backup.