Looks like there’s 1 million cables that connect from the solar panel to that EB3a. What cables do I need. And 10 foot extension

depends on what solar panel you have. If you have a panel with MC4 connectors you simple attach the solar charging cable that came with your eb3a to the solar panels and the other end to the eb3a. If you need an extension cable search amazon for “MC4 extension cable” in whatever length you require.