First, fetch either the Drupal 6 module, or the Drupal 7 module from their home on BitBucket This will bring a ZIP file onto your computer, decompress this file, and rename the resulting directory to “bmlt.” Install this in your sites directory. Once you have the module installed, go to the BMLT settings, and read this page for guidance on administering the plugin.
NOTE: You should always use this zipped file, as opposed to directly fetching from Git. That is because the project contains Git submodules, and Git does not recursively fetch submodules. You will end up with empty directories where the submodules are supposed to be.
Once the module is set up, then read this page to get guidance on how to make the BMLT instances appear in your articles.
You may also want to look at these pages for ideas and examples. They demonstrate WordPress plugins, but the process is almost exactly the same for Joomla! and Drupal.