If you can: via Google Play is best
If you have an Google account and Google Play on your phone the best place to download the app is direct from Google Play here. Or, if you have a barcode scanning app, you can point your phone at the following QR code:
If you can't access Google Play: you can still get the app!
Due to the model of phone you have, or the country you live in (e.g. China, Iran) Google Play may be unavailable. In this case you may download the app directly from here, or using this QR code:
Once you have downloaded the file, you'll need to go through a couple of steps to install it, this process is called sideloading:
1. Make sure "Allow install of non-market applications" is on. Go to your phone's main Settings menu, navigate to Applications then select Unknown Sources
2. You'll need an "apk installer" application (apk is just the file type of an android application). Most devices that do not have market access should have one of these already installed - most file managers will also do it. If you do not have one, you will need to use another service.
You can also install an apk file directly from your computer using the Android Debug Bridge (ADB). Our thanks to Berthold Horn for the following instructions:
Connect your phone usng the USB cable.
In 'Settings > Applications' check 'Unknown Sources'.
In 'Settings > Applications > Development'. check 'USB Debugging'.
If you have adb.exe installed on your PC, then, from a Command Prompt, type
adb install <<full path and name of the .apk fileto be installed>>
If the app is already installed on the phone you will get a complaint.
In that case, uninstall the old version using 'Settings > Applications > Manage Applications'
Invoked without arguments, ADB shows a command line summary, as well the version number (currently 1.0.26). Do not use very old versions.
(*) Putting the directory where adb.exe resides into your PATH may make it easier to call ADB.
(*) Making a batch file that calls adb.exe with 'install' as the first argument is convenient. For example, the batch file could contain just the lines:
(*) Finally, you may want to link the extension .adk directly to your batch file so that when you double click on a file with extension .adk it will automatically invoke 'adb.bat'. One way to do this is to right click on an .apk file, select 'Open With' > 'Choose Default Program'---
The "Android Debug Bridge" (ADB) comes with various programs, including e.g. Android Developer SDK, Android App Inventer, No-Root Screenshot, etc. Do a search for "adb.exe" to see whether there already is a copy on your machine.