As a start, I suggest learning the following:

Statistics:

- probability (distributions, basic manipulations)

- statistical summaries (univariate and bivariate)

- hypothesis testing / confidence intervals

- linear regression

Linear Algebra:

- basic understanding of arranging data in vectors and matrices

- operators (matrix multiplication, ...)

Calculus:

- limits

- basic differentiation and integration (at least of polynomials)

Information Theory (Discrete):

- entropy, joint entropy, conditional entropy, mutual information