Complete Newbie - GPG enryption/Kleopatra

Good morning. I’ve been asked to start using encryption software to send files to one of our vendors. I downloaded Kleopatra through the GPG4win site but have no idea what CAs or public keys are, and the more topics I read the more confused I am. Would anyone be able to provide a brief explanation of what these programs are and the best way to get started? It’s a simple Excel file that I need to encrypt. Do I start in the Excel file or somewhere else? Thank you!

Do you saw a tutorial?
You can use a public key-server for exchanging a keys but also you can simply transfer your open key by e-mail.