Normally, buildings unlock as your population grows. The option in this section gives you all of them from the start. When you want to plan the city you have in mind, try out a specific building or build a large-scale design, it makes the job easier.
Most codes here need cheats turned on first. See the section on how to open the console.
Content Manager > Mods
Every building, service and landmark becomes available without population requirements.
If you turn off the disasters option when starting your city, earthquakes, tornadoes and similar events never happen.