Geometry Nodes 3.0

Geometry Nodes — Blender Manual Read this first

Beginner

THis video talks about why Geometry nodes is a system that saves you time. He explains what an attribute is, and why they are important.

He goes over the basics, using different nodes to transform(move an object) and the join node to join 2 objects. He uses a convex hull node, and several others like subdivide to make the lattice around the objects.  He uses  naming and coloring of the nodes to better able to read the node tree, (a good practice for collections also), He talks about grouping too, which if you Group, name and organize will save you time later. (cntrl j to add a frame around your nodes, Press n for the side tool, name and label and color), his last tip, is that the top name of geometry node, is actually a group.  And if you add in another object and click on that you can use that group on that new object.

In this tutorial, He talks about how to add materials to your objects, and where you place the material node is important.  If you place the node at the right most part of the tree, the node will affect all the objects. (The monkey heads, and lattice)  If you put the material node before the join node, you can make multiple material nodes and place them after the node groups that are instancing objects, and Material node will affect whatever is in that group, like the Lattice group, or Monkey head group.      One tip I like is the that if you click on a node and hold on the alt key you can pull the node out of the node tree without removing the noodles.

This tutorial shows you how to use math in geometry nodes.  He uses a combine xyz node as a converter from a value node to a vector.  He then is able to use math nodes, He uses a math node with multiply and -1 as an invert node. A multiply connected to rotation and transform z.  If he uses a value node for rotation, you have to convert the say the number 360 to radians which is 6.28 .  (google that)  So for a full rotation using a value node use that number.  He also mentions that if you type #  that changes the input to frame, (as in the amount of frames in your animation.)  He does some more math to get how many rotations per frame is 30 frames x  60 seconds.  For a one minute animation, there are 1800 frames.  Divide 6.28 by that and that's how much rotation. He then shows how you can show the hands rotating faster using a math node with multiply.

He discusses which nodes to use to displace points.

He explores how to use instance groups instead of a value node.  So the columns, have a group of nodes that create the spheres, and the spheres have a group of nodes that make little droplets on the spheres. He is using simple shapes, but sets the idea of how to later on use objects or collections.

Intermediate

Erindale makes a grass field with flowers with geometry nodes 3.0.   A few more steps than 2.93 geometry nodes. (More nodes)   He first creates a plane  object and subdivides, and uses several nodes to displace the object so it looks like rolling hills.  Then he puts the grass and flowers onto the plane, making sure they follow the normal of the object. (so the grass points up following the terrain.) Then he uses some nodes to expose the density value of the flowers.  Sets the name to group, then sets the vertex group of the plane as group, and is able to weight paint the fowers onto this geometry nodes plane.  He also has a few tips about the new geometry nodes.  Remember to use cntl j to add a frame, or use the annotation to name your node groups.

A completely different idea of using an movie file to make geometry nodes.  He uses the string node to drive the text part.  

Default Cube makes a wreath in geometry nodes 3.  He basically adds a circle for the inside and another for the outside. Then make the leaf system of nodes. and the crucial node that links the torus object he made with the circles, and the leaf nodes, is the Instance on points node Which has an instance input.  He connects the output of the leaf system to that, uses a distribute points on faces to put them on the torus, sets a material and Merry Christmas.  (This tutorial really helped me figure out how to make something like a bush or hedge, thanks Default Cube)
 

Here is Part 2 from Default Cube.  He adds some ornaments and randomizes the color of the material. He does that by using the "realize instances" and "capturing attribute nodes".  That allows him to add an "attribute node" in the material shader, (as a bridge?) and then a color ramp with two colors with a mix shader of transparent and translucency. (you can use however many you want.)  I was able to turn off the realize instances node, and instead of using attribute I used an object info node, and the random setting, sped up rendering since instances instead of real geometry. He mentions how to make sure the instances don't intersect, On the Distribute Point on faces node, you select poisson disk instead of random.  I was wondering how to do that.   Excellent tutorial in that he sort of says why he uses certain nodes.  Sheds some light on Geometry nodes 3.

He goes over how to make a plant in geometry nodes.  A few issues, is the math.  If you multiply something by 0 the answer is 0 and you don't get the result you want.
He changes his value to .1 and then his node tree showed a result.  Something to remember when playing with Geometry nodes.  He goes over several nodes and why to use them.  Good tutorial for starting to learn Geometry nodes with math nodes. 

Advanced

Using the previous videos, you should be able to follow this tutorial.  

 Using the new geometry nodes 3 schema he shows you how to add objects and animated them using only geometry nodes.

This type of incredible effect is now achievable with Geometry Nodes. He creates a hexagon sphere by beveling an icosphere, and then uses geometry nodes with several node groups to create the effect.  Each node group section does a certain thing.  His thinking with geometry nodes is to break down each part of the effect into a node group section.  So he has to split the hexagons apart, then  have the bullet interact with the individual hexagons with a mask made out of color nodes.  And there is a  programing switch with a threshold he uses to activate the effect.  (compare)  He also has a section for the fade of the shield effect.  (This tutorial is Super Advanced and uses nodes that are very specific)

This person has a bunch of presets that do amazing things.  They are node groups.  Why doesn't blender have these by default?

Geometry Nodes 2.9 

Beginner

Using an empty to control the Geometry nodes height.

Long winded tutorial, but he has all the parts to make a great looking burger.  He uses geometry nodes for the seeds on the bun.

Intermediate

A use of geomery nodes that seems obvious.   Great tutorial

Advanced

He goes over a simple geometry nodes setup, and then a little about shading, and then compositing.  Nice little animation with good advice about compositing to save time.

He goes over how to model the objects, and using the geometry nodes, and even has some images and blend files as examples. He tells us why to use the different nodes also very helpful.  Great use of Geometry Nodes.