This thread may shed some light on tray manager.
Basically, a tray manager is used to keep the icons you'd like to see always visible and the ones you don't like, hidden.
Also notice that windows XP already does this, you can configure this, the main difference is that tray managers to this much better and some of them give you a menu with all the icons and their names (which would make it easier to choose one).
Here's how to configure the icons on your tray:
-Right-click your taskbar and select "properties".
-A new window comes up. Select "custumize", next to "hide inactive icons"
-A new window comes up. There, you can select which icons you'd like to "hide when inactive", "always show" or "always hide"
If you'd like to always show all icons, on the step where you pressed "custumize", don't press that, just untick that box "hide inactive icons" and press OK