Explanation:
the numerator (top part) of a fractional exponent means "to the power of ...".
the denominator (bottom part) of a fractional exponent means "the ...th root".
so,
(1/8)^(4/3) means the cubic root of 1/8 to the power of 4.
these 2 operations can be done in any sequence.
it is the same if we first put 1/8 to the power of 4 and then get the cubic root, or if we first get the cubic root of 1/8 and then put that result to the power of 4.
to keep the numbers small, I prefer here to start with the cubic root :
cubic root (8) = 2, because 2³ = 8.
and so, cubic root (1/8) = 1/2
(1/2)⁴ = 1/16
that's it.
(1/8)^(4/3) = 1/16