Google Docs need to be converted before uploading to a website.
From within the Google Doc Select File then Download and choose PDF Document (.pdf) or Word Document (.docx)
On a Chromebook your document will be saved to My Drive
On a desktop your document will be saved to the local Downloads folder
Login to the web page you wish to upload the file to. Use the web pages dialogue box to select the file you wish to upload from one of the above locations.