1)
The arrow for hiding the icons -
Right click an empty area of the task bar,
Select Properties,
Choose the "Task Bar" tab
Check the "Hide Inactive Icons checkbox.
Click "Customise" and
Choose the options according to how you want them i.e. Always Hide, Always
Show, Hide when InActive etc
2)
The icons appearing in the systray area are dependent on the programs you
have installed e.g. your Antivirus or Firewall etc might show an icon, among
various others.
What icon do you want to place there?
Come to think of it, are you talking about the systray notification area or
the "Quick-launch" toolbar?
If you want to add a short cut for an application to the quick-launch bar,
drag the icon you want to add and drop it on the toolbar.
If the quick launch tool bar is not showing, right click a blank area of the
task bar, select "Toolbars" and select "Quick Launch".