1. Press Ctrl-N to open the Navigator, and open up the "Indicators" tree.
2. Drag the indicator (e.g. RSI) into the relevant price window.
3. On the Parameters tab, set the "Apply to" appropriately:
a) if you want the RSI of price, choose "Close", "Open", etc
b) if you want the RSI of an indicator in the same window, choose "Previous Indicator's Data" or "First Indicator's Data"
(If you want to place the indicator in a separate window, instead of dragging in step 2, right click and select "Attach to a chart").