On where to start => I'd start by getting a very solid grasp of graph theory. It is the bedrock of many algorithms and along the way you'll learn all kinds of useful mathematical notation, but in a way that should be easier for you to pick up than plain old 'pure-math.' I've found the following series of videos presented by Donald Knuth, aka The Christmas Tree Lectures, to be incredibly informative and inspirational [1].

Another area of math that you need to know for C.S. related activities is linear algebra. To get started I'd recommend reading 'Coding the Matrix' by Phillip Klein.

[1] => https://www.youtube.com/playlist?list=PLoROMvodv4rNMsVRnSJ44...