First generate a vector $\mathbf{x}$ with independent $N(0,1)$ normal random components:
$$x_i \sim N(0,1).$$
Find the Choleski decomposition of the covariance matrix $\Sigma$:
$$\Sigma = L L^T .$$
Then $\mathbf{y} = L^T\mathbf{x}$ is jointly normal with covariance matrix
$$E(\mathbf{y}^T \mathbf{y})=E(\mathbf{x}^TLL^T \mathbf{x})=\Sigma E(\mathbf{x}^T \mathbf{x})=\Sigma I= \Sigma.$$
If the desired mean vector is $\mathbf{\mu}$, then use
$$\mathbf{z} = \mathbf{\mu} + \mathbf{y}$$