OpenSSL: You have to install that if it doesn't come preinstalled with your operating system (e.g. Windows does not have it preinstalled). How to install that depends on your OS (for Windows check the link provided by coder_For_Life22).
The easiest way without fiddling around is copying that openssl.exe binary to your keytool path if you are on Windows. If you don't want to do that, you have to add it to your PATH
environment variable. Then execute the command provided in the docs.
keytool -exportcert -alias androiddebugkey -keystore ~/.android/debug.keystore | openssl sha1 -binary | openssl base64
Note that the argument after -keystore
points to your debug keystore. This location also depends on your operating system. Should be in one of the following locations:
If you did everything right, you should be prompted for a password. That is android
for the debug certificate. If the password is correct the console prints a hash (somewhat random chars and numbers).
Take that and copy it into the android key hash
field inside the preferences of your app on facebook. To get there, go to developers.facebook.com/apps, select your app, go to Edit settings
and scroll down. After that, wait a few minutes until the changes take effect.