How do I import a key?

You have two options: import a key from a file or import it from a keyserver. It's probably most reliable to ask your contact to export their key into a file and send it to you.

If your contact has stored their key on a public keyserver, then you can import the key from the keyserver. You can use their email address to find their key, but it's more reliable if you use their fingerprint. If your GoodCrypto private server can't find the key on the keyserver, then ask which keyserver the key is on. Then ask your mail administrator to add that server to your private server.