Package the app (.apk file) by opening the project in the Designer editor.
Next choose Build > App (save .apk to my computer) from the top menu to download the .apk file. The option App (provide QR code for .apk) produces a scannable QR code that will download the app for two hours. You can share this code with others, but they have to use it within two hours of your generating it.
Once the build completes, you can email the app (.apk file) to your friends who can install it by opening the email from their phone.
NOTE: Anyone installing your app (which is an .apk file) will need to change the setting on their phone to allow installation of non-market applications: go to Settings > Security and then check the box next to Unknown Sources.