Was someone sitting on the seat with their foot on the brake when you pulled the string?
You can't start this mower by yourself if pulling the string.
Better instructions here:
Harbor Freight sells wheels that will work. It's just that they have 5/8" bearings that you need to change out to use 3/4" ID bearings
You will need a pair. Ace hardware sells them in their drawers, but they are expensive and eBay is about half price. Then you need some 3/4" fender washers to use as spacers. Once you have done that, if you ever need a tire or tube again, it's cheap, quick, and easy. Harbor Freight or any Home Depot or Lowes will have the parts handy.