You have two choices of tarballs, either the most recent stable release or the most current patch release. Stable releases occur a few times per year, and undergo more testing before release. Patch releases occur a couple times per month. The new contents in all releases are listed on the bug and feature page of the website.

Both tarballs include LAMMPS documentation (HTML and PDF files) corresponding to that version. The download page also has an option to download the current-version LAMMPS documentation by itself.

$tar -xzvf lammps*.tar.gz  This will create a LAMMPS directory with the version date in its name, e.g. lammps-23Jun18. You can also download a zip file via the “Clone or download” button on the LAMMPS GitHub site. The file name will be lammps-master.zip which can be unzipped with the following command, to create a lammps-master dir: $ unzip lammps*.zip