Making files 'searchable' is one of the most basic functions on LightRocket.
If you wish a file to be visible/findable for others you'll need to make it searchable.
Browse to My Files and Galleries and then to the My Files tab to view your uploaded files.
Then click on the LightRocket or internet (globe) icon to make a file(s) searchable either on LightRocket on your site or both. Here's a screenshot indicating the icons to click for making files searchable.
Note that if you add files to a gallery and publish that gallery on LightRocket or add it to your site, the files in your gallery will automatically be displayed as a part of your gallery but the individual files won't be searchable.
You'll need to specifically make each file searchable by clicking on the icons shown in the screenshot above if you want those files to be found searches either on LightRocket, on your site or both (if you click to activate both icons).