Hi beowulf, make sure to check out the tutorial videos here:
http://moi3d.com/1.0/docs/tutorials.htm

Those give a pretty good general introduction to the general methods used - you basically will draw some key profile curves of your shapes, then create surfaces from them, and cut/merge different pieces together.

Here is an overview of one way to make a helmet shape, I did this really quickly and it doesn't have proper proportions but I think it might give you some ideas on how to proceed.

I started by drawing a profile curve in the top view for the outline of half the helmet:



Then I switched to the 3D view, and held down Ctrl while dragging on that profile in the Z direction to make several copies vertically. I then turned on the control points of all these curves and adjusted the copies so that they tapered in somewhat as they moved upward:



Then create a surface through these curves using the Construct / Loft command:



Select the surface and use Transform / Mirror to make a mirrored copy of it, and you have the base shape of the helmet:



To make a slightly rounded top piece, I drew 2 curves that crossed each other, arranged like this:



Then I selected one of those curves, ran Construct / Sweep, and picked the other curve as the rail. This created a rounded sweep surface that looks like this:



This shape punches through the top of the helmet, the whole thing together now looks like this:



Now I want to merge those pieces together - select them both and run Edit / Trim, and at the "select cutting objects" prompt, push Done to do a mutual trim (indicating that these objects will act as both an object to cut as well as a cutting object itself). Select the outside bits to discard, and you are left with this:



Those surface pieces can now be selected and glued together by using Edit / Join.

Then to get a slightly rounded weld type shape, I selected the object an used Construct / Fillet to round off the sharp edges. Now it looks like this:




To make a kind of outward flare at the bottom, I selected the bottom edge curves, and use Edit/Join to create a longer curve object out of them:



Then I drew a small line segment in the side view that protruded out at an angle:




Then I selected that little line, ran Construct / Sweep, selected the joined bottom curve as the rail, and that created this flare thing at the bottom:



All together it looks like this now:



To put in the eye holes and grills you would draw some curves in the front view and then either use Trim on the helmet to cut it, or if you have made a solid you might extrude the curves into cylinder type shapes and then use a boolean to cut them away from the main helmet.


I hope this gives you some ideas on how to proceed - again the basic process is to draw key profile curves that define the shape, then use construction commands to build surfaces or solids from those curves.

You usually don't try to build everything all in just one single shot - notice how I built the side part of the helmet first and the top capping part later and trimmed them to each other. That is a typical method to build smaller pieces and combine them together using trimming or booleans, and round off the sharp edges between them with fillets.

- Michael