Dont know how to turn flash off on a samsung l100 camera.

http://www.samsungaccessory.com/product/Search.aspx?SearchWord=SAMSUNG%20L100

You don't. The flash is intended for still photography only, emitting a very brief burst of light. If you want additional light for videos, you'll need a separate llight source.

Most cameras flash twice; the first one is for setting the exposure, the second one is for real. About the best you can do is warn your targets that the camera is going to flash twice.

Yes, the L100 has a self-timer. Press Right on the selector (the clock icon) until the desired mode indicator appears on the display. Your choices are 10-second delay, 2-second delay, double self-timer, and motion timer.

The self-timer is described on pages 29-30 in my copy of the manual.

that should be on if your camera is plugged to your computer or charger.

There is the oclock icon on the round thing that called the dial control. The flash, flower, oclock, etc icons are on the dial control. The selftime icon looks like a oclock face.
Hit it one or more than one times and the icon will appear on LCD, so your done.
Should set the selftime at higher ( 10 second some like that ) that for you have time to be in the picture.

If the lens is retracted, hold up the camera to your eye and look at the lens. If you see one end sticking out a little bit, push that side in and press the power button. It should work.
If the lens isn't retracted, push the lens around until it is in its regular position. When you press the power button, it will retract and come out again and should work fine.

Hope this advice helps!

Samsung's have notorious problems with their lens-cap shutters malfunctioning. This seems to be the case with yours. It will have to be serviced, I'm afraid.

remove the memory card and slide up the lock at the side of it

have you check if you are using the usb cable or the av cable. the camera will not show anything on the screen if you are using the av cable and connect the camera to your computer.

The battery is located on the bottom of the camera. Plug the USB into the camera, and then instead of hooking it up to the computer, hook it into your adapter and then into the wall. When the camera is finished charging, the icon of the battery will be filled. I have the same camera.