Follow below steps to generate twitter keys and tokens:
Step 1: Navigate to Twitter Developer Apps Account
Step 2: Make sure that your mobile number is added otherwise it won't allow you to create app. You can add it from More -> Settings and Privacy.
Step 3: Click on Create an App button on top right corner
Step 4: Fill in all the required detail like: App Name, Application Description, Website URL, Most important is tell us how this app will be used because Twitter team will review your application and then only approve it.
Once it is approved, you can generate keys and tokens.