Module finds psd1 file in current directory (recursive) and pushes it to www.powershellgallery.com portal.
First it takes your API key to PowerShell Gallery from the MasterConfiguration.
Next it takes PowerShell Gallery name which is usually PSGallery, but can be different if you have your own configuration. You can check it using Get-PSRepository cmdlet.
In the last step it invokes Publish-ModuleTo cmdlet which pushes modules.
To use module invoke command in the directory of module.