It’s kinda easy, but not at first
Step 1:GO TO YOUR "MY GAMES "PAGE,> SHARE> EMBED> COPY
Step 2:MAKE AN HTML FILE WITH YOUR GAME’S EMBED, (NAME IT INDEX.HTML)
Step 3:PUT IT INTO A ZIP FILE
Step 3:GO TO YOUR NEWGROUNDS PAGE>UPLOAD CONTENT>UPLOAD YOUR GAME
Step 4/5: Click the upload button and select your ZIP
Finally, put information about your game, indicative rating, controls, etc…