First, create a Twitter collection within SearchBlox. This collection is only available starting with version 8.0.
Then, sign up to create an application at https://apps.twitter.com and make sure you have the following values for the Twitter application:
Access token secret
Under the Twitter collection settings, enter the values listed above in the appropriate fields.
Select Filter as the Stream Type, and then enter the values for Filter with Locations with the geo-location you wish to index.
For example, if you enter the following values:
-122.75,36.8,-121.75,37.8 // San Francisco
-74,40,-73,41 // New York City
-180,-90,180,90 //Any geotagged Tweet
this will index all tweets from within the geo-location bounding box.
See below for an input sample for a Twitter collection: