It's very simple, just follow the steps
Log in to Docs (www.docs.googe.com)
Click Upload ...
Click Select files to upload ...
Select the source files from your computer
Made sure that "Convert documents, presentations, and spreadsheets to the corresponding Google Docs formats" is ticked
Click Start Upload ...
When the upload is finished, choose Go Back to Google Docs
Open the file in Docs
Select the contents that you want to upload (possibly use Select All from the Docs menu)
Copy (you may need to use Edit / Copy from the browser, not from inside Docs)
Switch to the Blogger post editor, in Compose mode
Paste.
Add any other content that you want in your post.
Preview the post, and do any final formatting changes that are needed.
