Modelling with aluminium foil is very simple, but can be quite fun. It is probably best to start with something very simple and then try something more complicated later.
It will probably be too difficult to do the whole model with one piece of foil and so you may need to sculpt separate bits of the whole sculpture and then join them together. This might be tricky. To join the foil together, make sure that the end of the two pieces of foil are a bit loose so that you can wrap them around each other.
DO ASK YOUR PARENTS FIRST IF IT IS OK TO USE SOME ALUMINIUM FOIL. IT IS NOT CHEAP!!!
Below are some ideas for foil modelling.
This is how NOT to do it!