The Geometry Nodes-setup must be applied to a curve object. For cobweb to be generated, the curve object needs to contain splines. By the nature of how those splines factor into the web-generation, the location of the control points at the start and end of each spline are all that matters to the generator. For interesting web-structures to occur, multiple splines should be placed in proximity to each other within a single curve object. A nice way to play around with the setup, is to go into edit mode on a curve object, select the draw-tool from the panel on the left of your 3D-Viewport-window  (opens with "t") and select "surface"-mode for Depth. That way, you can make splines span across your preexisting objects with a drag of the mouse and quickly spin magnificent webs.

Now to the settings you're presented with in the Geometry Nodes-modifier:

• Material needs to contain the material, you want your threads to have.
  
• scale defines the scale of the features of the web. Think of it as the size of the spider that spun it. It affects the intricacy of the weaving. It equates to scaling the curve-object in "Affect Only: Origins"-mode (affecting the scale of the object without affecting it's contents in edit mode).
• thickness affects the thickness of the threads.
  

For the following settings, it is helpful to gain a rough understanding of the structure of the procedural cobweb. It has multiple levels of threads with increasing fidelity. Each successive level spans finer and finer threads between those threads already generated by previous levels or from existing geometry.

• density_lvl_## defines the density of threads of a certain lvl ##. Turn it up and more threads will be generated and spun to result in a denser (and often messier) web. Note that changing the density will also affect the existing threads.
• Seed_lvl_## will change the seed, based on which the threads are randomly generated. Shuffle through them to get different looks from the same base geometry. Regenerating a level with a new seed will also regenerate all subsequent (higher) levels as they are based on the levels preceeding them.
• particulate is a boolean value. Toggling it will enable the random distribution of spherical instances along the threads. This can be used to emulate dew drops or dirt particles gathering on the cobweb. All subsequent settings concern themselves with this feature and aren't relevent if it is not active.
• particulate_density defines the density of the particles.
• particulate_radius defines the maximum radius the particles will have.
• particulate_material should hold the material for the particulate (e.g. a glass material for dew drops).

The Node tree is made from reoccuring building blocks and node groups that are arranged in a fairly clear layout. Therefore, I also encourage you to go into the Node tree itself, to access more hidden settings and reconfigure the nodes to your liking.