Please have a look at this video. My question is, how can I make the animation in the video? Of particular interest is the selection of the region between two curves (delimited by the two parallel lines) and then extruded with rotation. Thank you in advance.
Once you've created your 4 curves, duplicate them, join the duplications with CtrlJ, right click > Convert to > Mesh:
In the Options panel enable the Auto Merge option and Split Edges & Faces (if you don't find this panel open the N panel > Tool > Options):
Now press G and Enter right away, it creates 4 vertices at the intersections of the edges:
Remove the useless vertices:
Duplicate the mesh, fill one version, use the other version to create the revolution effect with the Screw modifier (make sure to place the origin of the object at the center of the rotation, keyframe the Angle value to animate:
For the growing effect of your 4 initial curves, use the Bevel and the Start & End Mapping values as explained here.