Voter registration or enrollment is automatic in most advanced industrial nations, most of which are democracies, but is a requirement in many countries before a person is entitled or permitted to vote in elections. So it would be party registration.
Them is the topic of a text
The analogy is meant to show parallels between two sets of words. Fertile is to arable as vague is to clouded. If you understand either pair it can be used to decipher the meaning of the other pair you don't know.
He remembers the good ol' days.