A common question would be how to factorise into two brackets, for example x^2 + 5x = -6

The first thing you must do is get all the terms on the same side, which we do by adding 6 to both sides : x^2 + 5x + 6 = 0.
Next, we must work out which numbers add to the middle term, and write these down : 1 and 4, 2 and 3.
Then we need to work out the result of multiplying these pairs together, and see if any get the number we want, which in this case is 6 : 1 x 4 = 4 , 2 x 3 = 6.
So, we know that the numbers we need in our brackets are 2 and 3, as these multiply to 6. To finish, we simply write these numbers into the brackets (x + 2)(x + 3) = 0.