By far the quickest and easiest way to develop a plugin for e107 is to use the plugin builder ( Manage -> Plugin Manager -> Plugin Builder). It will create the plugin.xml (meta-data) file, as well as code most of the admin area of your plugin for you. Additional features may be added in future.
Steps to Use:
Create an empty plugin folder in e107_plugins/ (eg. 'myplugin')
Create a new text file with the _sql.php extension. (eg. 'myplugin_sql.php')
Using PHPMyAdmin, create your database table structure, and then export it in SQL format.
Copy/Paste the "CREATE TABLE" data to your your _sql.php file. (see other plugins for examples)
Go to Manage -> Plugin Manager -> Plugin Builder and choose 'myplugin' from the dropdown menu and then follow the prompts.
Thoroughly check the details of each Table Tab (and Preferences Tab if you need them) before proceeding with the creation process.