Navigate to "Dashboard" once you are logged in Moodle.

Click "Add" onto the dropdown to "Add a block" and select "Private files".

Add...
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The newly added block will be at the bottom of the block drawer. Click "Manage private files..."

Click add files and search your computer for files to upload.

Once files are uploaded, they will display in the "Private files" block.

How to Upload a File on Private Files block