Thanks for the question.
If you have a look at our Getting Started
online help article, you will notice that section called Create Series contains the following line of code:
Here you can see that getSeries() returns a collection or some sort of list because it has an add() method. You can call add() multiple times with more series and your chart will display all of them.
Check out the Telerik Platform - the only platform that combines a rich set of UI tools with powerful cloud services to develop web, hybrid and native mobile apps.