Ok I created an overlapping geomtries using Copy node.

But I want a single mesh, in other words each copied instance should have a UnionBoolean with the rest of the instances, ultimately becoming single mesh.

As you can see, these rings are overlapping, each copy of ring should have UnionBoolean with rest of the rings.

But I have no idea how to utilize ForEach node in this case..

:? ok let me make this more simple

How do you Cookie/Boolean groups of geometries generated using Copy node.

I dont know how to utilize ForEach node for this.

Look at how the Shatter SOP HDA is built. It uses For Each SOPs to boolean each successive result to each other.

If I were modeling this myself I would cookie/boolean one center ring with first the left and then the right ring duplicated using your final settings.
I would then duplicate the resulting boolean center ring using the same number of segments and rotation values as used to create the left-right rings to the one I was interested in.
This can be easily procedural-ised.

In this particular example I wouldn't rely on a boolean. Since you know the angle of rotation when you set up the copied rings, it is better to clip the rings at the proper rotation angle so that they match up perfectly.

Attached is a file with a torus set up to handle any number of rings you need. I have promoted a “# rings” parameter which you can work with at the object level. down below you can see a single ring cut using two clip sops then rotated and copied using a copy sop. The Number of rings drives the angle of the copy and also rotates a couple of simple lines. The end points of the lines are used to define the Direction of each clip. At the end the parts are fused to make them one surface.

Overall this solution is a lot more reliable than then boolean node (cookie) and you can set up as many rings as you need.

Thanks guys it really gave me a break.