Welcome to the forum. All programs come with a reference manual, though the quality varies a lot from program to program. So the first place to check is in the reference manual.
Code:
man sa
man head
man man
That will explain the default output and any options for modifying the output. It looks like the last column may be some program name.
Also, it helps with readability to wrap output in [code][/code] tags in your posts.
Which distro are you using, including version? And which package did "sa" come from?