To display an indicator on the chart, you need to enter its identifier in the symbol-search. The identifier consists of a two-letter country code (according to ISO 3166-1 alpha-2) followed by the abbreviated name of the indicator.
For example, the USGDP identifier stands for US GDP:
US - country code
GDP - abbreviated name (Gross Domestic Product)
You can also find economic data in the search either by the prefix ECONOMICS:
or by selecting the ECONOMICS exchange as the "source":
A complete list of available indicators can be found here.