First you need to disable demo footer block in 8theme options->general->footer then create footer manually using “8theme – Twitter Feed” widget.
Go https://dev.twitter.com/apps and sign in with your own twitter ID.
Click on the Create A New Application button;
Fill out the required fields;
After creating the app, click Create My Access Token button to generate the necessary codes;
Then will appear all 4 items you need: consumer key, consumer secret, access token, access token secret
Copy and paste each of those items along with your Twitter ID into the appropriate Twitter widget fields in Appearance > Widgets;
Push Save button.
If you get an error on frontend, please, check permissions on your wp-content/themes/classico/code/cache folder, it should be 777 with recursion.