Well, the way your asking this shows that you have no clue how hard and time taking it is to make even a simple mesh.
First, as Thierry said, you need some kind of 3D modeling program, like blender or AC3D. Blender is free, and once you know HOW to use it, its very easy, but learning is uh.... almost impossible Cx. AC3D is easyer i think, but it cost 80$. However, in the world of 3D modeling, a 80$ Program is CHEAP.
So, im guessing you will chose Blender xD. First, you have to download it (duh) so heres a link to the download
DA LINK **http://www.blender.org/download/get-blender/**
Ok, great, chu got blender, congrats xD. Now, if you open it, your brain will probly explode with all the buttons, tabs, and who-knows-what-else. So, you need to learn how to USE it, luckly, tutorials exist =D
I suggest going to youtube and looking for videos like "blender for beguiners" "Blender modeling basics" "Blender for dummys" Ect.
xD Modeling is NOT easy unless you know how to do it, even then, its not exactly a walk in the park.
