For a very useful video introduction on measuring tree ring widths using CooRecorder, see VIDEO: CooRecorder Tutorial by Stockton Maxwell at Radford University.

Note: You can turn on the English subtitles through the settings command in the lower right corner. You might reduce the Playback speed to e.g. 0.8 if you think that the video is running too fast. The Pause command is bound also to the "k" key on your keyboard which makes that command easier to reach for repeated use.

There is an alternative link available at Vimeo: "CooRecorder Tutorial")

Here is a follow-up by Stockton Maxwell with additional tips on using CooRecorder:
VIDEO: CooRecorder Tutorial Part 2

Still another introduction by Stockton Maxwell, now on using CDendro:
VIDEO: CDendro Tutorial