Congressional Apportionment is a process of aligning the voting districts to ensure that all eligible citizens are counted and given a political precient that will allow them to vote for a candidate. Every 10 years this process is reevaluated based upon the Census which tracks population growth and loss in each state and nationally.
We use the redistricting game: www.redistrictinggame.org
Gerrymanding is a process where political parties try to manipulate the voting districts so that their candidate will be most able to win election to the House of Representatives.
Gerrymandering can impact who wins election in the House of Representatives and the Senate, but Redistricting in general only impacts the amount of representatives that a state has allocated in the House of Representatives.