Registration is the act of enrolling in something, like a school. There is also registration for voters and drivers and people attending a conference.
In life, there are some things anybody can do at any time; for other things you have to go through registration first. Registration is the process of signing up or enrolling in something. Colleges make students go through registration to sign up for new classes. There is a registration process for voting: if you haven't registered, you can't vote. Registration usually involves some paperwork and waiting in line. No one enjoys registration, but it's something we all have to do.