Just to clarify: Do you want to graph the following function? :
g(x) = -√(x+2) + 2 where the (x+2) is the radicand (under the radical)
Do you know how to graph y = -√x?
If so, do you know how the (x+2) changes the graph of y = -√x ?
Then,...

Your question may be to complete the square to solve for x?
If that is the case, here is how you would go about doing that:
To complete the square on the left side of the equation, you want
to get a form of (x + a)2 on the left side. To do that, you want to
get a form of...

In general, the graph of f(x-h) will shift the graph of f(x) to the RIGHT h units.
In general, the graph of f(x+h) will shift the graph of f(x) to the LEFT h units.
In general, the graph of f(x) + k will shift the graph of f(x) UP k units.
In general, the graph of f(x)...