The rand function is for uniformly distributed random numbers, while randn is for normally distributed random numbers. Both functions accept arguments for the size of the output that you want:
>> A = rand(3,3)
A =
0.8147 0.9134 0.2785
0.9058 0.6324 0.5469
0.1270 0.0975 0.9575
>> B = randn(3,2)
B =
2.7694 0.7254
-1.3499 -0.0631
3.0349 0.7147
You can also overwrite a variable that already exists, so it sounds like you want:
variableX = randn(336,1);
This would overwrite what was in variableX with a new column vector of normally distributed random numbers, where the length of the vector is 336.
