In the 1940 the SS wanted to deport the Jews to various camps, usually death camps, through liquidation. The liquidation of the ghettos was basically a way of getting rid of the Jews in a systematic and orderly way. The occupants of the ghettos were systematically rounded up with the help of the Jewish councils running the ghettos. They were loaded onto cattle cars and made their way by rail to various camps.
This is a picture of all of the Jews lining up in up to get moved to the camps where they were either killed in the gas chambers of chosen for labor.