Access to the canyon is usually from Arequipa, the second largest city in Peru and often called the Ciudad Blanca (White City) for the white volcanic ashlar stone used for building. Arequipa is about five hours by bus or van over increasingly bumpy roads. Be prepared for high altitude as you'll cross 17,000' passes.
Tours can be arranged in Arequipa if you are not already with a tour group. You will probably stop for picture taking and a breather at the Salinas y Aguada Blanca National Reserve,
Busses go to Chivay and Cabanaconde on either end of the canyon, and you can begin your visit from either location. Many visitors choose to travel to Chivay, the biggest town in the canyon, in the afternoon, spend the night there acclimatizing to the altitude, and then tour Colca Canyon the next day.
You might consider staying at Parador del Colca Ecolodge, link below.