I accidently pushed to build something how do I stop it???

Click the "Delete" word underneath the build timer.

Unless it is a ship or defense, in which case you cannot cancel it.

-Istalris-

It is a ship... DANG IT... Also If someone attacked me and I defeated him/her how do I know how much debrie was made...

You would click on your planet in galaxy then hover over the debris and it will tell you

Here is one of my recent combat reports, as an example. The line in bold text is the amount of debris that was created. In this case, there was none.

Attacker Loss: 0 Defender Loss:0
winnings Metal:1.284.344 Crystal:419.220 Deuterium:127.982
Debris Metal:0 Crystal:0

EDIT: Sorry i just realized that doesn't show when you are attacked. You could see it if you click on the galaxy screen on the planet that was attacked, just like darklord says.

-Istalris-