tar -xvJf somefile.tar.xz
It is very annoying that so many are now using the .xz archive format as standard instead of .tar.gz but nevertheless above is how you would extract it with the "J" flag (not lower case j as that is for bz).
extract, xz, linux, centos, debian, ubuntutar, xvjf, somefile, tar, archive, format, gz, nevertheless, quot, bz,