1. Join Twitter here, if you're not already a member. You should enter your phone number when prompted.
2. If you already have a Twitter account, make sure you have a phone number attached to your account. (This is for verification purposes before Twitter will issue you a developer key.) To add a number, click your avatar on the top right of the Twitter home screen and click Settings. If you're logged in, you can also follow this link. On the Settings menu, select Mobile and enter a valid phone number.
3. While logged in to your Twitter account, go here and click "New" to begin the process of getting your API key.
4. Fill out the form. You will be asked for a website, but note that Twitter doesn't check if it's a real website or not as long as it's in this format: http://www.xyz.com
5. You'll be redirected to a new screen that shows the name you entered for your application. Click the tab at the top that says "Keys and Access Tokens"
6. You'll see your Consumer Key and Consumer Secret, which look like long strings of letters and numbers. Copy them to an empty text file on your computer. Make sure to note which is the Key and which is the Secret!
7. Nearly done! While still on the "Keys and Access Tokens" page, scroll all the way to the bottom and click the "Create My Access Token" button.
8. Under the "Your Access Token" heading, copy the Access Token and Access Token Secret and put them in the text document. You should now have four numbers: Consumer Key, Consumer Secret, Access Token Key, and Access Token Secret.