How do you multiply 2 square roots?

just put the product under the root symbol.

√2 * √3 = √(2*3) = √6
√8 * √18 = 2√2 * 3√2 = 2*3√(2*2) = 6*2 = 12
(note that √(8*18) = √144 = 12)

Did you have something a bit more complicated?