If I use optical flow Kit with px4 firmware on pixhawk then can I do autonomous takeoff, autonomous waypoint navigation indoors without GPS?
If yes then how do I enable the autonomous feature. I have installed optical flow kit. But it does not go in auto takeoff / position control mode.
Yes you can, but it is not out-of-the-box like GPS autonomous flight, you have to start with http://dev.px4.io/flow_lidar_setup.html
You have also to calibrate the lens, and sensor. See Arducopter doc for information http://ardupilot.org/copter/docs/common-px4flow-overview.html (It is not the same as you are using PX4 but it may help to understand)