If you’re interested in learning math on your own, like mind maps, but don’t know where to start, I highly recommend giving Learn Anything a look. It is a fully open source search engine, so you can also contribute back to the project. It also has mindmaps for a number of other subjects.
Another great resource for understanding different topics is Khan Academy. It covers a wide range of material from Early Math to Calculus. Their YouTube Channel is also a great help.
If instead you prefer perusing notes that work you through examples give Paul’s Online Math Notes a look!