Editor: To say it straight in only one sentence: gpg4usb is a very easy to use portable-application, which combines a simple text-editor with a GnuPG-frontend to write, Encrypt and Decrypt your text-messages. gpg4usb should work on almost any computer you're working on, should it be a Linux-machine or even one with a Microsoft-OS running.
Almost the only thing required is an available usb-port you are allowed to access. With this application you can write safe and encrypted messages anywhere you are: should it be an internet-cafe, at work or somewhere else on holiday... and you always have the encryption-keys available for usage!
The usage of gpg4usb should be highly self-describing, since the user-interface and all the options it offers are clear cut: Simply execute the binary on your usb-pendrive and start typing e.g. the Mailtext you want to be encrypted. If you're done, choose the right gpg/pgp-key for the person you are writing to and hit the encrypt-icon at the top of the application-window. The resulting encrypted text you can save as a text-file to send it as mail-attachment, or copy it directly into your mail-user-agent or webmail-website. To make sure, you can read this message by yourself afterwards, Encrypt It for the recipient and to yourself at the same time - if you want, you can mark as much keys as you want to encrypt for.
You want to add a gpg/pgp-key to your mobile KeyRing? Nothing's easier than that: just hit the crypto-menue-entry and choose Import Key from File or Import Key from Editor. This means that it's possible to import an ascii-armored pubkey via file-dialog, or via copy&paste into your editor-window. If you find a key e.g. on a website, just copy it, Paste It into the gpg4usb-editor and hit Import Key from Editor - that's it, and the key shows up on your keyring!