Please explain BiS stuff to me

[Malzian]

I'm not a troll.. I genuinely want to know so that I can keep improving

Then I refer you back to my comment below:

BiS is a mathematical meta designed specifically for min-maxing of stats in order to optimize the output (damage typically, but can also be healing and such) of a particular job. The issue with trying to be "BiS", though, is that it can actually be situational to the fight so one duty can have one BiS build while another can have a different BiS build. On top of this, you generally only need to be BiS for 2 things: FFLogs and Savage progression raiding. If you're not doing either of these than BiS doesn't much matter.

All of that being said, if you want to figure out your BiS you can always use the tools on http://ffxiv.ariyala.com