How to extract all the frames from a video using FFmpeg?

I want to extract all the frames of a video into a folder. I’ve heard that FFmpeg is the tool for the task but don’t know how to do it.

You heard correctly, FFmpeg is the right tool to achieve your task. You can use the following FFmpeg command to extract all frames from a video
ffmpeg -r 1 -i file.mp4 -r 1 folder_name/frame_%04d.png

Why is this " -r " flag used?

So basically, there is no frame rate for a collection of image files. Use “ -r “ before the input if you wish to under sample the video file.

Is it possible to resize a particular image of the frame of a video or what if I wish to take the screenshot image in ffmpeg?

Yes, For resizing the image:

Use the -s flag in the command

ffmpeg -i file.mp4 -s 640x480 %04d.jpg
For screenshot add -frames:v 1 in the command as shown below:
ffmpeg -ss 00:00:04 -i filemp4 -frames:v 1 screenshot.png