Factorising expressions
Factorising is the inverse of multiplying out a bracket.
To give you a quick idea - look at the expression that you are factorising and look for the highest common factor - the biggest thing that divides into all the terms.
For example, to factorise ax2+4x, x divides into both terms. x2 goes into the first term but it doesn't go into the second. 4 goes into the second but not the first. So the highest factor that you can find is x, and the full factorisation is
x(ax+4)