If you call GPG without input, it just says
gpg: Go ahead and type your message ...
You can enter text and everything, but how do you end the input? I've seen something like this in multiple different programs, but I've never known how.
You need to input EOF (End Of File). Do this with CTRL+D (or more generally,
Without any flags, gpg assumes you want to decrypt, expects an encrypted message, and will output the results, in binary, to stdout.
If you want to encrypt something and deal with the result in a practical way, try
gpg -ea and then type some secret message, then cntrl-d and give recipients, when asked.
You can then copy the ascii-armored message to the clipboard which you can paste into a file or whatever.
If you relauch gpg without flags and paste that message in, it will ask for recipient's key passphrase, and then wait for you to close stdin... type ctrl-d and your message will be decrypted to stdout