Machu Picchu tickets CANNOT be purchased when you arrive at the ruins. Instead you have to get your entrance tickets in advance. You can purchase your ticket in two different ways:
1) – Online
Go to the website: https://machupicchu.center to buy Machu Picchu tickets online
You can see the availability of Machu Picchu tickets in real time.
You can get your machu picchu pass far in advance, specially if you intend to go to Wayna Picchu (or Huayna Picchu) since only 400 people per day are allowed to go up there (2 groups of 200).
2) – In Person
When you arrive in Cusco, visit the Instituto Nacional de Cultura (INC), close to Plaza de Armas
Machu Picchu Tickets Pricing
For full pricing details of Machu Picchu tickets please visit: Machu Picchu ticket prices and cost