To protect your camera from damage while shooting an eclipse, one needs a filter that attenuates infrared energy as well as visible light. Standard neutral density filters do not necessarily attenuate IR at all. It's not totally clear to me from the link for your filter that it is a proper solar filter or not. Before using a filter on your camera to take pictures of the sun, you need to positively confirm that the filter is effective against UV and infrared wavelengths as well as visible light.

It should go without saying that the filter needs to be placed in front of the front element of the lens. For larger telephoto lenses with "drop in" filter holders near the back of the lens, most of the glass and other parts of the lens will not be protected.

You will need the solar filter in place anytime the camera is pointed directly at the sun with any kind of telephoto lens attached. The sun will be bright enough that you will still be able to see it to focus using magnified Live View. I would recommend making some kind of shade to allow you to look at the camera's LCD screen and controls without exposing your eyes directly to the sun. I use foam board with a hole cut just large enough to fit the barrel of my lens through.

For a more about solar filters, please see this answer to What kind of filter do I need for safe sun photography?
How do I photograph the sunset without damaging my camera?
Can the sun damage the camera sensor? Under what conditions?