Good questions as this is what you bought the H for. Much of what follows is very basic stuff but in covering it I hope to answer potentially unasked questions.
On the right side of the screen to have the camera and video camera icons as you noted. You must select one or the other of them for the type of imagery you want to generate. You cannot take a still picture while in the video camera mode, and vice versa.
The camera icon permits still photography, the video camera icon establishes video mode. To the lower right of the screen is the button that starts and stops video. You must push it once to start and again when you want to stop a video. To the lower left of the screen is the button that triggers the shutter. A quick push activates them, don't hold them down. The game style controls on the ST-16 do nothing so don't bother with them. Before you start doing anything video go into "System Settings" on the ST-16 and touch the "Camera Select" button. That should bring up two or three camera selections. Choose "C-GO3-Pro". That allows generating stills in higher resolution. Start out using a "Natural" video setting in order to review videos in a condition that best displays how you did with the other camera settings like white balance, EV, shutter speed, and ISO. Each has an impact on the video and still image product. Note that camera settings are not available until the camera has been turned on.
Something you may find helpful is setting the H up on a table outside somewhere to allow power up and view of the surroundings without having to fly. Practice using the various camera settings without having the props turning. Better yet, remove the props to avoid accidental arming. The battery lasts a heck of a lot longer and you are not putting your H at risk by being airborne with the inevitable early fumbling with camera setting functions.
As for how to use the different camera settings, YouTube is our friend and saves many key strokes in explanation. I'll start you out with this one, along with a big thanks to CaptainDrone for making it:
I suggest you spend as much time as you can in learning how your camera works, and in how to set up shots. Watch lots of YouTube photography videos and keep the sun to your back unless you can deal with lens flare. Along with all that you will need to learn about video editing if you have not done any before. It's something that is always changing so you can never learn enough. Photography is a skill requiring constant practice and much learning. Obtain a notebook you can jot down what the settings were for different photos and videos you made to allow references you can learn from. Were they washed out, over saturated, whites looked off color? What settings were used to cause that?
