PermaStore is a general-purpose multi-part binary storage standard for Antelope
For a sample web application that retrieves PermaStore files from the blockchain, check out PermaServe.
To download or upload files to PermaStore, one option is to use the standard cleos command-line tool that comes with Antelope implementations. Then it's just a matter of understanding what all the actions on the PermaStore contract do, which can be gleaned from the pstore.cpp source file.
Another option is to use the storeos command-line tool. It is a single-file Perl script that can be downloaded from the root directory of the PermaServe repository. Run the script without arguments to see the tool help.