How to set materials to geometric objects using MatLab?

Hi,

I am quiet new to Comsol.
I am activating Comsol server via Matlab interface.
I build everything using Matlab commands (LiveLink for Matlab).

I am modeling a system of one object (solid) inside another object (liquid) and solve for heat transfer (part of the solid is heated). I built three geometrical objects: the liquid (a box), the solid that is not heated (a cylinder with a missing part) and the solid that do heat (the missing part).
I created two materials - 'liquid' and 'solid'.
I can't find a way to "attached" the materials to the geometries.
The example in the help files - the 'Busbar model' present a similar task but solve it with some kind of selection which is not exactly explained.

How should I I connect each geometrical object with the material which it suppose to be made of?

Thanks,
Alon