How do you join 2+ verticies into a single vertex?
Scale the two together as small as you can. Then, with both still selected hit w and then remove doubles.
Shift + S, 4, Shuft + S, 2, W, 4
Martin
I push W and all it get is subdivide and switch direction.
You’re not modelling with polygons. Just select one vertice and delete it and the curve will remain without that single vertice.
But I want the curve to be an entire circle, without any break. It there is a break, the render looks stupid cuase there’s a big open spot all the wat along the cave wall.
press ‘c’
Damn, I amde a lot of typos. Thanks the c key was what I was looking for.
No problem! 
Btw., ‘c’ stands for Close!
To join two points to form a curve press ‘f’. ‘c’ only works for the last segment hence ‘close’. I think ‘f’ stands for ‘face’ from the mesh editing aspect of blender where you can use it to create edges and faces.
I made typos talking about my typos.