Trial and error.
Various methods were tried, especially when it became clear that shooting was detramental to those doing the shooting. Eventually gassing was found to be the most cost effective and most humane (to the executioners).
To kill the Jews
Yes, they did.
Yes, they killed millions of Jews.
The Jews
holocaust
the Nazis would kill them
yes
any that were available.
The Nazis would kill the Jews and thae Jews would hide and runaway like mice.
for power and to kill Jews
6 million jews
the question suggests that the Nazis killed Jews for weakness, this does not make sense, weakness was not a cause. Please rephrase.