More detailed information about elections in New Zealand can be found on the Electoral Commission website, elections.org.nz
Your party vote
Your party vote is important because it helps decide the share of the 120* seats in Parliament that is allocated to each political party. If a party crosses the minimum ’threshold’ (either by winning at least one electorate seat, or 5% of all party votes) it has seats allocated to it in close proportion to the percentage of party votes it receives. A party's share of seats is filled first by candidates who win electorate seats and then by candidates from the party list.
Your electorate vote
Your electorate vote helps decide who your local member of Parliament will be. There’s a different choice of candidates in each of the 64 general electorates and seven Māori electorates. Each candidate usually represents a political party, but a candidate may stand for election independent of a party. The candidate who wins the most electorate votes wins the seat.
Voting outcomes: overhang seats
‘Overhang’ occurs when a party wins more electorate seats than the total share of seats it would otherwise be allocated based on its share of party votes. The overhang seats (the number above the party vote entitlement) are added to the usual 120 seats until the following general election.
Voting outcomes: the 2017 General Election
At the conclusion of the 2017 General Election there were five political parties represented by 120 members of Parliament in the 52nd Parliament. There were 49 list, 64 general electorate, and seven Māori electorate members of Parliament in the House of Representatives.
When an electorate seat becomes vacant between general elections a by-election is usually held. Only eligible voters within that electorate can vote, and there is no party vote. Under some circumstances, such as if the next general election is less than six months away, an electorate seat may be left vacant. This requires the agreement of 75% of the House.