I'd like to recommend GPG4Win. It's an open source software that run's on Microsoft Windows. It contains a tool called Kleopatra which provides a really nice GUI interface for managing keys. It doesn't require any technical knowledge to use. It's also quite powerful as you dig deeper into the application.
Gpg4win enables users to securely transport emails and files with the
help of encryption and digital signatures. Encryption protects the
contents against an unwanted party reading it. Digital signatures make
sure that it was not modified and comes from a specific sender.
Gpg4win supports both relevant cryptography standards, OpenPGP and
S/MIME (X.509), and is the official GnuPG distribution for Windows. It
is maintained by the developers of GnuPG. Gpg4win and the software
included with Gpg4win are Free Software (Open Source; among other
things free of charge for all commercial and non-commercial purposes).
*Note: This screenshot came from a German version, there are other translations including English
And if you have the Outlook desktop client, you can use the Outlook Privacy Plugin. It works directly with PGP4Win so you can manage your keys there and then encrypt/decrypt from this plugin. (This is what I use, highly recommend it:)