Save the indicator in the following folder
C:\Program Files\Interbank FX Trader 4\experts\indicators
If you save the indicator while the Platform is open you will have to close it and open it again. To use that indicator go to the Navigator window and select the indicator and click on it to attach it to the chart.
If you download a new indicator save it in the following folder
C:\Program Files\Interbank FX Trader 4\experts
If you save the expert while the Platform is open you will have to close it and open it again. To use that expert go to the Navigator window and select the expert and click on it to attach it to the chart. When a window pop ups select "Allow live trading". Also, make sure the Expert Advisers icon on the top of the platform is depressed (blue hat with green right arrow).
If you made any changes to the Indicator or the expert compile it by hitting F5 key.
here are some links that have some useful tips
http://www.interbankfx.com/tutorials.php
http://articles.mql4.com/197
http://www.forexfactory.com/showthread.php?t=12151