The Hajj is the grand pilgrimage to Mecca. All Muslims who have the means and opportunity are supposed to make the Hajj once in their life.
With improved economic welfare and greater ease of transport, more people want and are able to come every year than can be accommodated. Saudi Arabian authorities have therefore established quotas of pilgrims from each country. For people who have the opportunity to go, there are many practical details to be arranged: buying tickets, finding a hotel, getting vaccinations and visas. To this end, there are authorised travel agencies that arrange package tours which include a guide and sometimes include pre-travel meet-ups.
The best preparation of all is to plan to be very patient indeed. For a brief period, many people from every corner of the world gather in Mecca. It is often crowded, with many hours of waiting.