Having a difficult time setting up a new printer, HP ENVY6455e with my MacOS 10.12.6 Sierra operating system

When networked with either Ethernet or Wi-Fi, the Envy 6455e is supported by Apple's built-in AirPrint, and does not need any HP software or drivers. With AirPrint, the scanner support comes from Apple's Image Capture. AirPrint does not support a USB direct connected printer, or in this case, a multi-function device by USB.

The optional, paid VueScan Professional software also supports scanning on this device without any Apple or HP software/drivers.

If you have networked your Envy 6455e, and it is powered on, visit System Preferences > Printers & Scanners panel and right-click on the Printers entry for the device, and select Reset printing system… from the secondary menu. If you haven't set it up, and the Printers panel is empty, click the + symbol for add a printer…

In either case, a Add Printer panel will appear, and your Envy 6455e should show a Bonjour detection indication. For Use: Choose AirPrint instead of the HP drivers, and then click the Add button. The following was taken from macOS Big Sur where the appearance mode is dark. Yours will be light.

Since you have told us nothing specific as to what problems you are having, it is difficult to give you the right response. The link below is where HP provides its driver for this unit. However, they do not say whether it works with your OS. Have you tried installing it? Your operating system is very old and the available HP driver may not work with it. You may have to look at upgrading your operating system to a newer version. What, if any OS can be installed depends on the year and model of your Mac, which you haven't provided. Since this is apparently a combination printer/scanner, you may have to install a third party scanner app such as VueScan. It is well supported and works with most all scanners. You will have to confirm that their software will work with your older OS, however. There is a one time cost for it, but you can try it for free. I recommend it and have purchased it for myself. I have no association with VueScan.

https://support.hp.com/us-en/drivers/selfservice/hp-envy-6400e-all-in-one-printer-series/2100178605/model/2100187516