There is a lot going on here. So let's go over it.
You see the video I'm watching on the left, and my TubersLab notepad on the right. By the way, I didn't have to open it up manually. Once you install the Google Chrome/Firefox extension, it just shows up.
I went ahead and added 2 timestamped notes for you to see what it looks like with and without the option of a screenshot.
My first timestamped note is on second 0.17, "MKBHD is showing the iPhone 12". I didn't pause the video manually; it happened automatically as I started typing.
P.S. To play or pause the video at any time without using your mouse, simply hit the 'alt' key. So once you're done with your note, hit alt or press play to continue watching.
The second option, and my personal favourite, is using the alt and control buttons.
As I already mentioned, alt plays/pauses the video. But control adds a screenshot, like in the image below.