This tutorial covers indicator installation for MetaTrader 4. If you need info on how to install MetaTrader 5 indicators, please, read my Indicator Tutorial for MetaTrader 5.
There are many free MetaTrader indicators available
1. Download custom MT4 indicator and save it to the ‘Indicators’ folder of your MetaTrader’s data folder. It can be found at the following location:
2. If it’s already compiled (.ex4 file) then fine, if not (.mql file) — double click it with your mouse and it will be opened in MQL editor (this editor is standard for every MetaTrader 4); click the ‘Compile’ button at the center top of the editor window — the indicator will be compiled and ready to be attached. There might be some errors or warnings during the compilation, but in most cases there shouldn’t be any. You can try and fix those errors, but usually it takes some time and programming skills to do this.
3. After you get the .ex4 file in your indicators folder (through compilation or download), you can start using it with your MetaTrader platform. All you have to do is to attach it to the chart. If you know what you are doing you might also want to change some of the indicator’s input parameters.
OK. Now you can enjoy your new MT4 indicator and hopefully — better Forex trading results.
Update 2014-02-06: Updated directory information relevant for MT4 Build 600.