This bus has a "change" at Victoria station on the way to Canterbury. Does that require leaving a bus at Victoria Station and boarding another bus at Victoria for the last leg to Canterberry? How does this work?
Yes, you change bus. You get off the bus from Heathrow in the Arrivals Hall, collect your luggage, go through the signposted covered walkway, and cross Elizabeth Street to the departures hall on the other side of the street.
You should enter in the middle of the departures hall- Stands 1 to 10 (ish) are on your left, 11 upwards are on your right- all numbered and with seating.
There are toilets in both sides of the departures hall, and stands to grab a bite to eat and a drink.
Overhead monitors tell you which of the 20 or so stands your next bus is departing from. When it is time to board (usually around 15 minutes before departure) the doors to that stand are opened, you present your ticket to the driver on your device, who will then place your luggage in the hold of the bus.
If you have chosen to reserve a specific seat then that seat will be labelled as reserved. On the right hand side of the bus (facing forwards, driver side) the rows are numbers 1 upwards, on the other side from 2 upwards, as row 1 is the wheelchair space.
On the monitors you are looking for the 007 to Dover or the 022 to Ramsgate- Canterbury is one of the en route stops- the previous one being the University of Canterbury. All stops will be announced by the driver.