Can not find? Most tutorials are not specifically for vanilla Gmax, but for specific game pack like Trainz or Microsoft Flight Simulator. Much of their tutorials teach basics how to use Gmax. Gmax is based on 3ds Max 4, search Max 4 tutorials and they match pretty well.
For starter it is difficult to start modeling biological forms with all legs and hands. Doing simple stick-men or buildings, barrels, letters, gets you going.
Keep your vertices (triangles, polygons) count down when doing so simple models, they do not need high definition.
Of course keep up your spirit, for first try it is rather abstract and even bit advanced (all these angles and different shapes with smoothness). You learn quick, by playing you learn