This is the fourth article from the series "MQL4 Languages for Newbies". Today we will learn to write custom indicators. We will get acquainted with the classification of indicator features, will see how these features influence the indicator, will learn about new functions and optimization, and, finally, we will write our own indicators. Moreover, at the end of the article you will find advice on the programming style. If this is the first article "for newbies" that you are reading, perhaps it would be better for you to read the previous ones. Besides, make sure that you have understood properly the previous material, because the given article does not explain the basics.