4
You don't "upload" a block.
You "Add Block" which creates a new custom block.
There you add new "Content" which is your HTML and/or PHP code
You also specify where this module is "Visible in" - for testing purposes the best it to select "All Pages"
Click "Submit" and your new block should be visible, unless the code you've entered in "Content" has bugs.
I am finishing updating "
XOOPS Operations Guide" which hopefully will be helpful to you in these situations. You can download it
here