Let's take everything step by step, then.
You have (1/16) raised to the power -1/4. We should tackle the minus first. That minus over there basically tells us that you should "flip" the fraction, turning 1/16 into 16/1 or 16. This is what a negative power means: just tun it over!
The general rule is that (a/b)^(-n) = (b/a)^n.
Now, let's see what we get: (1/16)^(-1/4) = 16^(1/4). Now, this 1/4 actually stands for the fourth degree root of 16, which will be 2, since 2^4 = 16. Following this rule, we get that sqrt(n) = n^(1/2). It's just another notation for roots.
The general rule over here is: a^(1/n) = the n-th degree root of a.
Let's take some more examples:
81^(1/4) = 3 (the fourth degree root), since 3^4 = 81
8^(1/3) = 2 (the third degree root), since 2^3 =8.
64^(1/6) = 2 (the sixth degree root), since 2^6 = 64.