how to make avatar carry a prim and place it on top of another prim?

[Rolig Loon]

That's not easy at all, if you actually mean that you want an av to carry the prim in its hands and then place it somewhere.  Doing that would require a custom animation and a bit of scripting.  It would be much easier if you bypassed that step entirely, since the important part of the exercise is what happens on the circuit board. Just have the person drag  or rez the component to any one of a dozen or so predetermined spots on your circuit board (perhaps by clicking on the spot to identify it with a function like llDetectedLinkNumber or llDetectedTouchPosition, depending on the design of your project).  The rest of the job -- telling whether that was the right spot and notifying the person -- is trivial scripting.

[Rolig Loon]

That's not easy at all, if you actually mean that you want an av to carry the prim in its hands and then place it somewhere.  Doing that would require a custom animation and a bit of scripting.  It would be much easier if you bypassed that step entirely, since the important part of the exercise is what happens on the circuit board. Just have the person drag  or rez the component to any one of a dozen or so predetermined spots on your circuit board (perhaps by clicking on the spot to identify it with a function like llDetectedLinkNumber or llDetectedTouchPosition, depending on the design of your project).  The rest of the job -- telling whether that was the right spot and notifying the person -- is trivial scripting.