When you have a function (say f(x)), you can translate it left or right by replacing what's inside the function. In this case it is shown that the x in f(x) is replaced with x+2 in g(x). Therefore:
Rewriting g(x) like this shows that there is a +2 in the f(x). Whenever there is a number being added inside the function, then the graph is shifted left that many units (and vice versa for subtraction). So in this case since 2 is being added inside the function the graph will be translated left 2