Start Fetch by double clicking on the Fetch icon on your hard drive or on Mac_Software. Then:
To download files from your web account to your mac, simply select the file and press the get button.
To upload files from your mac to your web account, press the put button and select the file to upload.
Note: Make sure you select the right file type, Raw Data is for pictures, movies, sound files etc. and Text is for text files. (This will normally be done for you if you have the 'auto' button selected in the information window.) Also, make sure that the extension is correct--sometimes Fetch will try to change your file names from name.html to name.html.txt.