ex4 files are compilled mq4 files. They can be EAs or Custom Indicators. So, you have to know what exactly is your file in order to copy it in the correct folder. If it is an EA you have to copy the file in ....\MetaTrader\experts\. If it is an Indicator you have to copy it in ....\MetaTrader\experts\indicators\.

If it is an indicator it should work with no problems after you attach it to the chart (unless there are errors in the code). If it is an EA you have to enable the use of Expert Advisors from Tools - Options - Expert Advisors. You also have to check "allow live trading" from the dialog box that appears when you attach the EA to the chart.

Tell me if it works.