Can someone explain to me how to use voxel
gdevelop is a 2d engine and does not support voxels.
the only way to make use of voxels in a 2d engine is by making sprites out of your 3d voxels and use the sprites as images for your animations.
The most useful way to use them would be a technique called Sprite stacking, see here for an example made with gdevelop, and this post, for a game:
there are tools, like this Website where you can export your 3d models as sprite stacks.
if you are interested in this method you can find guides that explain it pretty well. but be aware that this method is heavy on resources and building an entire game around it can only go so far.