The VvE's articles must set out how many votes each apartment owner can cast at the meeting (article 5:112(2)(d) BW). So it is not always one vote per apartment: a larger apartment can have more votes.
Under the Model Regulations 2017 the owners are entitled to vote, and the total number of votes and the number per owner are in the deed (article 51). With a long lease (erfpacht), the leaseholder in principle exercises the vote (article 5:118a(3) BW). If an apartment belongs to several people together, only one of them (or a third party designated in writing) casts the vote (Model Regulations 2017, article 52.1).
You can also have a proxy cast your vote. With a sub-division, the board of the sub-association casts the votes (article 5:127(3) BW).
See also: Proxy (volmacht), Quorum, Absolute (simple) majority, Sub-division (ondersplitsing), Fraction (breukdeel)
Read more: Quorum and majorities in a VvE
Legal basis: Boek 5 BW, art. 5:112, 5:118a, 5:127, Modelreglement 2017, art. 51–53