Here's one way to think of it: if A^(1/N) = B, then B^N = A.
For example, if

, then

, so X is 16. Does this help?
The other part of your question has to do with order of operation. Always do the exponents before multiplication (unless there are parentheses or brackets, which override). So, your original question was 12 times x raised to the 1/4, written out as:

must be thought of as:
 )