Put the extracted files in the worlds directory of your Minetest installation directory. The files such as env_meta.txt must be directly in the world's directory (eg. worlds/my_world/env_meta.txt).
On Microsoft Windows, downloaded package distributed by celeron55, or use a RUN_IN_PLACE version, your worlds directory is:
minetest-base-directory/worlds
If your Minetest is a system-wide installed version on GNU/Linux, your directory is something like (create if needed):
~/.minetest/worlds
Map authors: .zip or .tar.gz format is preferable, please avoid .rar format when possible.