To complete the square on ax^2 + bx + c.

Firstly take out the coefficient of x^2 as a factor: a(x^2 + (b/a)x + (c/a)).

Next write the square of x plus half the coefficient of the x term: (x+b/2a)^2

Then add and subtract the constant term of that: b^2/4a^2: a((x+b/2a)^2 + c/a-b^2/4a^2)

Then simplify: a((x+b/2a)^2 - (b^2-4ac)/4a).

In your case: a=1

x^2+4x+6 = (x+2)^2 + (6-4) = (x+2)^2 + 2.

The relation between the graph of y = x^2 and the graph of y = (x+2)^2 + 2

is a left shift of 2 (x -> x+2) and an upward shift of 2.