The steps to uploading a file...

Find the upload section, then click on 'browse'.

Navigate your way through your folders until you find your 'index.html' file.
Double click on it, or click on 'open'.

The name of the file will be in the 'source' section,
you will need to click your mouse in the 'target' section
to enter the name of the file once it's uploaded.
If it doesn't enter automatically when you click in the box,
you will need to type 'index.html' in.

Hit 'upload', and wait for it to do so.
The page will refresh when it's uploaded, with the 'index.html' file in the list!!