OPTIONAL: You might want to make a new free Trello account for your bot. It's easy to switch between accounts and it saves confusion down the track.
Get started by going to the setup page.
Make sure you're logged into Trello with your bot account (or your account if you're using that) and get your Trello API key from here.
The token is generated especially for your API key. The link to get it will appear below the input field after you have put in your API key.
If there are any problems and we need to identify you, we will use this email address. Please use the email address associated with your bot's account in Trello.
Press "GO" and you're done. The next step is to run a simple “action” against the Trello API to test out your new bot.