"Status availability" is one of those qualities. It'll appear as a green bubble next to a user's photo. Other users will be more likely to respond if they discover someone who sent a tweet is online, which will lead to more conversations. You can use the reply button if you need any help.

In the social sidebar Twitter search field, enter the geocode: operator, followed by the latitude, longitude and radius (in miles) that you would like your search to include, in quotation marks (e.g., a search of geocode: “43.643513,-79.397639,1mi” would return Tweets within a one-mile radius of the Live Toronto office ...

If you use a desktop browser, you'll see Search Filters on the top right section of your screen. For mobile users, you need to tap the first icon next to the search bar. It looks like two swords. In Search Filters, left-click Near You under the Location section.