Extracting ONE image from video in Photoshop

I'm a beginner with Photoshop and I'm trying to extract an image from a video. I've learnt how to do so by rendering the video at the wanted position in the video. The problem is that I don't know how to find out the correct Start and End frame.  On the timeline, you can just see the frames for each second. How can I select the correct Start and End frame to make sure that I capture a photo at exactly the right spot?

Many thanks,

Caspar