Connecting your Github account to Geckoboard can be a little tricky as there are a number of fields and it may not be clear what you put where. Below are the instructions for what to enter in each field.
Github account is your username.
Your API Key can be found in your account, you just need to copy and paste it.
If the URL is https://github.com/ONE/TWO then you need to enter ONE in the Github organization field and TWO in the Github repository field to connect your account properly.