I've recently finished tackling differential equations. I want to start learning general relativity, but from what I've read, I need to have a firm footing in differential geometry first. So where do I start learning DG? I really don't want to do a half-hearted job in an attempt to quickly jump onto GR, so does anyone know some good websites where I can properly practice it? It is out of portion stuff for me so I don't have any book to refer to, but I want to do it anyways. I would also love to know the difference between topological analysis and differential geometry.