The Ultimate Mathematics Search Engine:
https://www.wolframalpha.com/
And the Wolfram Math Encyclopedia:
https://mathworld.wolfram.com/
How and where to learn mathematics:
A good channel for learning about and exploring mathematics is:
Numberphile:
If you like a nuts and bolts approach to hard core mathematics check out:
NJ Wildberger:
More interesting math topics include:
https://en.wikipedia.org/wiki/Group_(mathematics)
https://en.wikipedia.org/wiki/Dynkin_diagram
https://en.wikipedia.org/wiki/Coxeter%E2%80%93Dynkin_diagram
https://en.wikipedia.org/wiki/Coxeter_group
https://en.wikipedia.org/wiki/Weyl_group
https://en.wikipedia.org/wiki/Lie_algebra