Well at ten you are getting an excellent early start.
Look at the original post, see how most of the model is basic shapes, cylinders, cubes.
Everything is duplicated symmetrically.
So to practice, make basic shapes, block together the parts, save them.
Once you have the parts all saved, block together a model by duplicating and placing, save that.
Go back to your parts and one by one perfect them.
Go back to your blocked model select whole parts, get their positions, remove them, import your new better shapes, and set them in place.
Start simple, with cool things like say this gun turret with cylinders.
or this turbolaser with cubes and cylinders finished up with greebles.
or an ion cannon, spheres, cylinders, and a touch of greebles
or the power generators
Practice makes perfect, start simple and someday you'll be amazing.
When I was your age all I could get were dinky plastic or die cast metal toys, what a waste of time and money.
To live out my Star Wars dreams I had to trace snow speeders and walkers from a model instruction sheet on notebook paper. Or play
this awful video game, without Halo music.
Wish I was ten with a computer and AC3D...man.