Factorisation involves finding and 'taking' out factors of equations.
For example, if we have the equation we can see that both parts to this equation have a common factor of , we can therefore write this as:
As you will know from very early maths, if two things multiplied together equal 0, then one of them is zero.
Using this fact we can then state that either
This can also be applied to quadratics, a quadratic equation such as
can be factorised to
This is a slightly different method, but there is a good article on factorising quadratics here.