Click on the file you want to encrypt with the → in the pop up menu. You will then be prompted with the Public key selection dialog. Choose the key of the recipient and click . The encrypted file will be saved with a
.gpg extension depending on whether you chose ASCII armored encryption or not. ASCII encrypted files only use readable characters to represent the data resulting in files that are more robust when copied around or sent by mail but are one third larger.
You can encrypt the contents of the clipboard by selecting the item in applet menu. When you choose then the text will be signed instead. Both actions will import the current clipboard contents into an editor window, perform the requested action and paste the contents back into the editor.
This is as simple as clicking on the button. You will then be prompted with the Public key selection dialog. Choose your key and click . The encrypted message will appear in the editor window.
Usually you can only encrypt files with keys that are trusted by you. Since you sometimes want to just send a confident note to some random people you are aware of having a GPG key you can set the option Allow encryption with untrusted keys.
To make sure that you can decrypt every file you have encrypted even if they are encrypted with someone else's key you can use the options Always encrypt with and Encrypt files with which are available in the KGpg configuration.
For more information on the encryption options ASCII armor, Allow encryption with untrusted keys and Symmetrical encryption, please refer to gpg's documentation or man pages.