Typically, dry-docks (in terms of regular cruising) are planned times when a cruise ship is taken out of service. There are times when a cruise ship's dry-dock is unplanned, but these situations are rare and usually occur after a major problem. Once a cruise ship has finished its last cruise prior to dry-dock and disembarked all passengers, the cruise ship will travel to a facility that has a dry-dock. When the cruise ship arrives, this dry-dock area will be filled with water and the ship will be able to slowly sail in. Before the water is drained, measures will be taken to make sure the ship is secured in place. This can be done by placing blocks under the ship. Each facility or shipyard may have a slightly different way of doing this, so please realize processes may vary.
Throughout the time in dry-dock, the ship will be receiving different types of work. Some things that occur during the dry-dock will be changes that are visible to the cruise ship's passengers. For example, cruise lines often use dry-dock times to add new features or renovate places onboard. In some cases, cruise lines just use the dry-dock time to refresh public areas by deep cleaning surfaces, replace carpeting, or do things that are hard to do when the ship is normally in service. Other areas of work that may occur during a dry-dock may not be directly visible to the cruise ship's passengers. A cruise line may decide to have the ship's hull painted during dry-dock or get some mechanical parts replaced. Although passengers cannot see these things, they are still important to keeping the ship functioning properly.
If you know a cruise ship is going into dry-dock you may be curious about what will be done to the ship during this time. I recommend calling or emailing your cruise line and asking if any information can be disclosed about the changes that will be made during dry-dock. In many cases, cruise lines will say more information will be coming later. This could mean the cruise line is planning on putting out a press release or details are not finalized yet. It never hurts to try to find out information.