The best programs for opening and editing PSD files are Adobe Photoshop and Adobe Photoshop Elements, as well as CorelDRAW and Corel's PaintShop Pro tool.
Other Adobe programs can use PSD files, too, like Adobe Illustrator, Adobe Premiere Pro, and Adobe After Effects. These programs, however, are mainly used for video or audio editing and not as graphics editors like Photoshop.

If you're looking for a free program to open PSD files, I recommend GIMP. It's an extremely popular, and completely free, photo editing/creation tool that will open PSD files. You can also use GIMP to edit PSD files but could run into problems since it has issues recognizing complex layers and other advanced features that might have been used in Photoshop when the file was created.

Paint.NET (with the Paint.NET PSD Plugin) is another free program like GIMP that can open PSD files. Other free photo editors support opening PSD files as well, and some can also save to the PSD file format.

If you want to quickly open a PSD file without Photoshop, I highly recommend Photopea Photo Editor. It's a free online photo editor that runs in your browser that not only lets you see all the layers of the PSD, but also do some light editing...although nothing like what Photoshop provides. You can also use Photopea to save files back to your computer in the PSD format.

IrfanView, PSD Viewer, and Apple's QuickTime Picture Viewer—part of their free QuickTime program—will open PSD files, too, but you can't use them to edit the PSD file. You also won't have any kind of layer support because they just act as PSD viewers.

Apple Preview, included with the macOS, should be able to open PSD files by default.

Note: If the program that automatically opens PSD files on your Windows computer isn't the one you want to open them by default, changing it is pretty easy.