You may want to review fractional exponents first.
Fractional exponents are often easier to work with than roots. Therefore, you should be able to rewrite an expression with roots so as only to involve fractional exponents. For example, 4√(√(2xy − 2)) can be rewritten as ((2xy − 2)1 ⁄ 2)1 ⁄ 4. You can then use the usual laws of exponents to rewrite this as (2xy − 2)1 ⁄ 8.
Note that, in this section of the website, I don't expect you to do any other simplifications. In fact, please don't; the computer will get confused.