i ma new to blender...i have two faces...while i enable snap to face with tick the project on to self and project individual elements...and hit g and enable proportional editing...the below surface overlap the upper ones...while i want upper surface cover below surface without overlapping..but the final screen is like this
This is a classic caveat of snap-to-face. I'm assuming you have it set to "closest". All vertices will snap to the closest face to the camera. In this instance, it has the side effect of causing some vertices which were previously on one side ("below") of the surface to snap above it.
A mesh isn't explicitly always a proper shape; so we have to watch for these things, and outside of looking at normals, all vertices look the same internally. So non-manifold meshes are unfortunately perfectly possible here, and the tool is actually working as intended. So let's look at how we get around your problem...
The best way around it is to snap it one side at a time—only select the vertices closest to you, snap them, then change your view position and move on to the rest. (If you're fortunate and only have two sides to worry about, you can press Control+I to simply invert your edit mode selection; then switch sides. It's hard to say how that will work for your torus, though.)
Another option is the Shrink Wrap modifier, which also allows you to fit one mesh over another and even provides an offset. If this sounds complicated, you might see if Shrink Wrap does the job better for you!
Speaking of meshes not always being proper shapes, the last thing I can suggest—bearing in mind that I'm not sure what your end goal with this project is—is to try out some of the non-mesh shapes like a NURBS torus or a curve. They have their own issues, but they don't have this one, and when you have your final shape figured out with them, you can press F3 and "Convert to Mesh"; and it will produce a mesh matching that shape.
Welcome to the community!