As of 2018, you must get into Library > Tools in Steam, then use the search feature for 'Creation' in that section the tool is no longer listed otherwise. Moreover, it is only available on the PC, as console manufacturers do not allow third-party content to run on users' systems.
However, the download (approximately 81MB in size) is only visible to users who have already bought the game.
It can be located on Steam under Library > Tools > Skyrim Creation Kit. The Creation Kit is available for download through Steam and its current version is v1.9.36.0. The Creation Kit is an external program that is run separately from the game of Skyrim. The tool was released on 7 February 2012, along with the High Resolution Texture Pack. The Creation Kit or CK (known in previous TES games as the Construction Set or CS) is a tool that can be used to view and edit the game's data files.
