Domain and range of the function f(x)= a sqrt(x+h) + k

From http://www.xtec.cat/~ebraso/visual/funcions/doraradic/dorara.html in catalan The DOMAIN AND THE RANGE Move the green dot
Investigates and responds: Which of the 3 parameters (a, h or k) is what determines the Domain)? What is the function parameter depends on increasing or decreasing? If you change the value of the parameter a without changing the sign, changing the domain? It modifies the range? If you not change a, which parameters (h or k) determines the Range?