The Upload button will open a dialog as below. Press the Browse button to open a file explorer in your computer's operating system. Since the exact appearance of this will depend on your computer type the instructions can only be general in nature for this one. In this dialog you need to navigate to where you saved the Mara distribution download. (You did download our fantastic product, didn't you?)
You don't need to extract the zip contents. Just upload it as is.
The CPanel dialog asks what permissions to apply to the uploaded file. Just accept the defaults. Which are usually 644. (In other words you the accountholder can change the files, others can read them)
At bottom right, you should see a progress bar..
When finished you can return to the file manager, and should see the zip file in public_html.