Run the R script run_analysis.r. It downloads the zip file and uncompresses it, if it doesn't exist in the direcotory where this file is. If the zip file is in the folder make sure the unzipped folder UCI HAR Dataset is also in the same directory, this is done to avoid downloading and uncompressing each time the script is run.
It produces the file tidy_dataset.txt.
The codebook is in the file codebook.md of this repository.