Use the noun causation to talk about the process of causing something to happen. If you try to sue your brother for your bike accident, you’ll have to prove causation.
It’s easy to remember what causation means if you break it apart. Most of the word cause is in there, plus -ation, which you might recognize as a noun suffix that describes an action or process. So causation is the action of causing something. It’s a formal word, and you'll often hear it come up in legal or scientific contexts. If you become a research biologist, you might do experiments to determine causation of a particular kind of cancer.