Working with concrete

Well... here it is at last... I have started working with concrete... and discovered that I'm going to need to hunt for a lot more moulds! I started by filling a mould with water in order to give me the right amount of concrete, but even with pouring most of it on the floor (see pics!) I still made much more concrete than I needed for that one mould. I'm also cheating with three moulds but sticking extra bits on polystyrene over "holes" in the mould. I'm just hoping that the concrete comes out easily, and I can re-use the moulds.