It depends what you are reading, but a good discrete math textbook provides a lot of groundwork for mathematics commonly used in computer science, but expects little in terms of prerequisites, so notation is usually explained.
At some level, learning the fundamentals is just necessary, but for computer science discrete mathematics and linear algebra (the basics of which are easy and also don't have much in terms of prerequisites) will get you far.
On the other hand higher math is ruthlessly cumulative. If you find that you need to understand Lagrange multipliers, for instance, you'll see they relate to the gradient, which has its own symbol, which is defined in terms of partial derivatives, which have their own symbol, which relates to limits of vectors, which have their own symbols and notations, etc.