**definition**

Let $A$ be an $n\times n$ matrix. Then for $t\in \mathbb R$,
$$e^{At}=\sum\_{k=0}^\infty \frac{A^kt^k}{k!}\tag{1}$$

But in this definition, What they are meaning by the term $A^kt^k$, If I give this matrix $$A=\begin{pmatrix}1&-1\\2&3\end{pmatrix},$$

what can we say about the $(1)$, means How it will be?