By default port 0/1/2 & 0/1/3 are stack ports. So, all you need to do is connect DAC/optic cables to these ports.
And if you are looking to use the first two ports (0/1/0, 0/1/1) as well to be used as 'stack ports', then you "reclaim" then via below CLI:
add stacking interface stack <module/port>
ex: add stacking interface stack 1/0
add stacking interface stack 1/1
And if required, make them normal ports using CLI: 'delete stacking interface stack <module/port>'