The cardinality of any set is the size of the set or the total number of elements present in the set.

For a given set $A$ Power set of $A$ is set of all the subsets of set $A$

Let $P=\left\{0,1,2\right\}\implies P(A)=\left\{\phi,\left\{0\right\},\left\{1\right\},\left\{2\right\},\left\{0,1\right\},\left\{0,2\right\},\left\{1,2\right\},\left\{0,1,2\right\}\right\}$