A neighbor installed a new bathtub faucet for me. At the point the shower connects to it, it is leaking badly. How can I fix that?

The shower connects in several places. The shower raiser connects to the valve body, the shower arm connects to a drop earred ell in the wall and the shower head connects to the chrome shower arm. That's three joints. Which one leaks? Or is it something else? Give us a explanation and more details. Tom

It is leaking where the pipe attaches to new faucet. Thank you.

It is leaking where the pipe attaches to new faucet. Thank you.
This is a picture of a shower valve,(see image) The top opening is where the shower raiser attaches to the valve. Is this where it's leaking from? Tom

Yes, that's it. Thank you Virginia

The most obvious answer would be to ask your neighbor to uninstall the riser pipe and to reinstall it correctly. If it is threaded he needs at least 3-4 full wraps of white teflon tape. If it is a sweat fitting he needs to reheat the connection, completely clean both parts removing all solder and then resolder withflux paste.

Thank you, Virginia