Try this explanation:
this is quadratic function (parabola, common view of equation is y=ax²+bx+c).
Domain: The function exists in all the points. It means, that x∈R or x∈(-oo;+oo).
Range: according to the common view a>0, it means, that parabola has 'min' in its vertice (x₀=-1). Range is y∈[4;+oo) or y≥4.