Buffs are positive effects on your character, shown as a green icon.
Debuffs are a negative effect on your character shown as a red icon.
A few icons relate to a changed state of your character which is neither positive or negative, these are shown as blue icons.
These icons are shown in the Buff Bar, opened in the classic client through a blue button on the expanded Status Bar, top left corner
In the enhanced client there are two bars which can be locked in place on the desktop.
In both clients these bars can be rotated by clicking on the corner blue button