Where do I take moments from in a question? I;ve been told I can take them from anywhere but this doesn't make any sense to me?
You will often take them at a point where you don't know something For example, if you don't know the mass of a beam then take them at the centre of mass of the beam. If you don't know the tension in supporting strings, then take them at one of the strings so that tension there can be ignored and you can solve the tension in the other string.