The easiest way to share your plugin is to put it on the WordPress.org site. Read the WP Plugin Hosting About Page. Be sure you understand the implications. Highlights are:
Your code must GPLv2 compatible. This means it is open source.
You will need to check in your code to the WordPress.org Subversion repository
You can’t do nefarious things
Then when you are ready, apply to add your plugin.
NOTE: In the Plugin Name field, you want this name just right. They will take your name like “My Awesome Plugin” and create the identifier “my-awesome-plugin“. This identifier because the top level directory of your plugin, and the URL to your plugin on the site will be “http://wordpress.org/extend/plugins/my-awesome-plugin/”.
When you generate the code for this plugin template, it assumes this will happen. So when you put “My Awesome Plugin” in the form to generate the template code, the generated code is in directory “my-awesome-plugin”, and in the my-awesome-plugin.php file in the header at the top, you will have:
Plugin Name: My Awesome Plugin
Plugin URI: http://wordpress.org/extend/plugins/my-awesome-plugin/
Text Domain: my-awesome-plugin
So you want to make sure these all match.
Subversion Code Repository
Next you need to get your code into the WP.org Subversion (SVN) repository. Your SVN URL will be something like:
Check out this directory from SVN, naming it at your plugin’s top level directory (like “my-awesome-plugin”) instead of “trunk”. Put the contents of your existing code directory (like “my-awesome-plugin”) into this directory. Add all the files and sub-directories and commit. Make this your working version and commit changes as you make them.
You may want to use a program that helps you use SVN. On Windows, TortoiseSVN is good (and free).
Making a Release
Refer to Versions and Releases. The “Stable tag” line in your readme.txt file (the version of this file on the trunk) tells WP.org which SVN tag has the “released” code. That is what will be available to people in the WP admin consoles.
If you navigate to your Plugin’s WP.org home page (like http://wordpress.org/extend/plugins/my-awesome-plugin/) you will find a link to Forum Posts (a link like http://wordpress.org/tags/my-awesome-plugin). This is the place where users can post questions and bugs.