Hi Rudy, Shell can be found under Construct / Offset / Shell.

It is used to create an object with a "wall thickness".

There are 2 ways it can be used. One way is to construct a solid of the specified thickness out of a surface:

Here you see a surface to the left, and to the right the result of using shell on it to thicken it to a solid:



One thing to be aware of is that if you have any tight curves or bends in your surface, you can't generally use a thickness value that is greater than the radius of the bend, otherwise this will cause the calculated surface to sort of fold back on itself.

Then the other way to use shell is as a way to sort of "hollow out" a solid. On a solid you can select faces of the solid which will become openings, and then after you run shell on it, you will have an object with wall thickness. Here's an example - this is the result of taking a box, selecting the top face and then running shell:



You can see there how the selected face becomes an opening, and all the other parts of the box became slabs of the specified thickness.

It is also possible to shell a solid without selecting any faces, in which case it will hollow out a cavity within the solid. But generally when used with solids you first select a face for the opening.

Let me know if you have any additional questions about shelling.

- Michael