I want to create a helical/spiral structure like the figure below. I tried to create a circle and poke faces after that I dont know how to extend it in z direction to look like a spiral.
You can use the 'screw modifier' to do that.
Here is two examples, just starting with an edge (segment) a bit rotated and placed differently relatively to the objects origins:
The modifier starts with a base mesh and extrudes it around an axis (of the mesh itself or the one of another object). The 'screw' parameter give the elongation along the axis.