Like the others say, a PhD is learning how to do research so you're not expected to know how to do it already.
I think it's useful if you can say why you like doing research. Break it down into specific things you enjoy eg being responsible for your own work, planning your own time, whatever is applicable to your discipline. and if you can link it to longer term i.e. career aims as well that will help show why you are motivated.
the grades you got for your project and refs from project supervisor will also be important.