In Kdenlive, how to select an area for render? In Kdenlive's render settings I can choose the option to render "selected zone".

How do I select the zone? 

"Shift + left click" enables a box selection. However it only selects whole clips, so this approach does not work.
Use the keys "i" for "start" and "o" for "end" to create the selection. They use the current frame position.



Example:

Move the playhead to frame 190 and press "i". Move it to 390 and press "o".

This creates a selection with beginning at the frame 190 and end at 390.