The Size and Shape of the Supercell

There are two ways to specify this. Cartesian coordinates can be used

%BLOCK LATTICE_CART
units

$R_{1x}$ $R_{1y}$ $R_{1z}$
$R_{2x}$ $R_{2y}$ $R_{2z}$
$R_{3x}$ $R_{3y}$ $R_{3z}$

%ENDBLOCK LATTICE_CART

Where, for example, $R_{2x}$ is the x-component of the second lattice vector and $R_{3z}$ is the z-component of the third lattice vector and so on.
The supercell can also be defined in terms of the magnitudes of the lattice vectors

%BLOCK LATTICE_ABC
units

$R_{a}$ $R_{b}$ $R_{c}$
$R_{\alpha}$ $R_{\beta}$ $R_{\gamma}$

%ENDBLOCK LATTICE_ABC

$R_{a}$, $R_{b}$ and $R_{c}$ are the magnitudes of $\bm{a}$, $\bm{b}$ and $\bm{c}$ and $R_{\alpha}$, $R_{\beta}$ and $R_{\gamma}$ are the values of $\alpha$, $\beta$ and $\gamma$.

In both cases if [units] are not specified default units of Å are automatically used. However, angles must be specified in degrees.