I've been trying to figure this out for several days now but nothing online is helping so I'm just going to ask specifically and hope this helps. I am currently creating a low poly giraffe and would like to animate it. I created armature and parented it so the mesh does move properly when I move the bones. But when I try to generate the rig, it doesn't create those loops and stuff. It only shows the circle on the floor with the four arrows. I have tried all sorts of stuff but for the life of me can't figure out how to do this. Hopefully someone can help me out, it would be much appreciated:) (Beware, I've clicked quite a few things in the program which may have cluttered stuff and made it more confusing idk)
Rigify uses the so-called Meta-Rigs to generate the actual rig. The Meta-Rigs is used to tell Rigify where the bones are located and how your model looks like.
The generation of the rig fails because you try to create a metarig armature from scratch and haven't defined any of the needed rig types for the bones. These define various parts of the rig (leg, spine, neck, face, tail, etc). It's a kind of module/building block and the metarig object is built from these.
Long story short, you don't need to create a Meta-Rig from scratch because there are predefined Meta-Rigs. Use one of these and adjust it to your model.
I would choose the Horse for the giraffe:
This gives you a skeleton of a horse:
Now, scale it a bit down so the legs have roughly the same height. Apply the Scale with Ctrl+A.
Switch to Edit mode, and move the bones. You can select the linked ones with L if you select one and hover the mouse over it.
Do not delete single bones! You need to delete the whole rig type. Better just move them into position even if you don't need them.
Beware, the neck and the spine are not connected. (3D Cursor in the screenshot). But these bones must stay together else the generation of the rig will fail with an error. Use Lasso or Box selection to select them both.
If you have separated them accidentally you can use the 3D cursor (Shift+S) to move the head of the neck.001 bone to the tail of the spine.006 bone.
(This is the very first giraffe I've rigged. The layout of the bones might be not correct.)
Finally, generate the rig armature and bind the mesh to it (Ctrl+P, Parent To > With Automatic Weights).